IceCream-Cpp is a little (single header) library to help with the print debugging in C++11 and forward.
Contents
- Install
- Usage
- Pitfalls
With IceCream, an execution inspection:
auto my_function(int i, double d) -> void
{
std::cout << "1" << std::endl;
if (condition)
std::cout << "2" << std::endl;
else
std::cout << "3" << std::endl;
}can be coded instead:
auto my_function(int i, double d) -> void
{
IC();
if (condition)
IC();
else
IC();
}and will print something like:
ic| test.cpp:34 in "void my_function(int, double)"
ic| test.cpp:36 in "void my_function(int, double)"
Also, any variable inspection like:
std::cout << "a: " << a
<< ", b: " << b
<< ", sum(a, b): " << sum(a, b)
<< std::endl;can be simplified to:
IC(a, b, sum(a, b));and will print:
ic| a: 7, b: 2, sum(a, b): 9
We also can inspect the data flowing through a range views pipeline (both STL
ranges and
Range-v3), by inserting a IC_V() function at the
point of interest:
auto rv = std::vector<int>{1, 0, 2, 3, 0, 4, 5}
| vws::split(0)
| IC_V()
| vws::enumerate;So that when we iterate on rv, we will see the printing:
ic| range_view_63:16[0]: [1]
ic| range_view_63:16[1]: [2, 3]
ic| range_view_63:16[2]: [4, 5]
This library is inspired by the original Python IceCream library.
The IceCream-Cpp is a one file, header only library, having the STL as its only
dependency. The most immediate way to use it is just copy the icecream.hpp header into
your project.
To properly install it system wide, together with the CMake project files, run these commands in IceCream-Cpp project root directory:
mkdir build
cd build
cmake ..
cmake --install .If using Nix, IceCream-Cpp can be included as a flakes input as
inputs.icecream-cpp.url = "github:renatoGarcia/icecream-cpp";The IceCream-Cpp flake defines an overlay, so that it can be used when importing nixpkgs:
import nixpkgs {
system = "x86_64-linux";
overlays = [
icecream-cpp.overlays.default
];
}Doing this, an icecream-cpp derivation will be added to the nixpkgs attribute set.
A working example of how to use IceCream-Cpp in a flake project is here.
The released versions are available on Conan too:
conan install icecream-cpp/0.3.1@If using CMake:
find_package(IcecreamCpp)
include_directories(${IcecreamCpp_INCLUDE_DIRS})will add the installed directory within the include paths list.
After including the icecream.hpp header in a source file:
#include <icecream.hpp>all the functionalities of IceCream-Cpp library will be available by the functions
IC, IC_A, and
IC_V; together with its respective counterparts IC_F,
IC_FA, and IC_FV; that behave the same but accept an output formatting
string as its first argument.
The IC is the simplest of the IceCream functions. If called with no arguments it will
print the prefix, the source file name, the current line number, and the
current function signature. The code:
auto my_function(int foo, double bar) -> void
{
// ...
IC();
// ...
}will print:
ic| test.cpp:34 in "void my_function(int, double)"
If called with arguments it will print the prefix, those arguments names, and its values. The code:
auto v0 = std::vector<int>{1, 2, 3};
auto s0 = std::string{"bla"};
IC(v0, s0, 3.14);will print:
ic| v0: [1, 2, 3], s0: "bla", 3.14: 3.14
The variant IC_F behaves the same as the IC function, but accepts an output
formatting string as its first argument.
To print the data flowing through a range views pipeline (both with STL
ranges and
Range-v3), we can use either the IC_V or
IC_FV functions, which will lazily print any input they receive from the previous view.
The IC_VF function behaves the same as IC_V, but accepts a format
string as defined to the range types as its
first argument. Since these functions will be placed within a range views pipeline, the
printing will be done lazily, as each element is generated. For instance:
namespace vws = std::views;
auto v0 = vws::iota('a') | vws::enumerate | IC_V() | vws::take(3);
for (auto e : v0)
{
//...
}In this code nothing will be immediately printed when v0 is created, just when iterating
over it. At each for loop iteration one line will be printed, until we have the output:
ic| range_view_61:53[0]: (0, 'a')
ic| range_view_61:53[1]: (1, 'b')
ic| range_view_61:53[2]: (2, 'c')
Note
The Icecream-cpp will enable its support to Range-v3 types either if the "icecream.hpp"
header is included some lines after any Range-v3 header, or if the ICECREAM_RANGE_V3
macro was declared before the "icecream.hpp" header inclusion. This is discussed in
details at the "third-party libraries" section.
The IC_V function has the signature IC_V(name, projection), and the IC_FV function
IC_FV(fmt, name, projection). In both them, the name and projection parameters as
optional.
The same syntax as described at range types format string.
The variable name used to the view when printing. The printing layout is: <name>[<idx>]: <value>. If the name parameter is not used, the default value to <name> is
range_view_<source_location>.
The code:
vws::iota('a') | vws::enumerate | IC_V("foo") | vws::take(2);when iterated over will print:
ic| foo[0]: (0, 'a')
ic| foo[1]: (1, 'b')
A callable that will receive as input the elements from the previous view and must return the actual object to be printed.
The code:
vws::iota('a') | vws::enumerate | IC_V([](auto e){return std::get<1>(e);}) | vws::take(2);when iterated over will print:
ic| range_view_61:53[0]: 'a'
ic| range_view_61:53[1]: 'b'
Note
The IC_V function will still forward to the next view an unchanged input element,
exactly as it was received from the previous view. None action done by the projection
function will have any effect on that.
Except when called with exactly one argument, the IC function will
return a tuple with all its input arguments. If called with one argument it will return
the argument itself.
This is done this way so that you can use IC to inspect a function argument at calling
point, with no further code change. In the code:
my_function(IC(MyClass{}));the MyClass object will be forwarded to my_function exactly the same as if the
IC function was not there. The my_function will continue receiving a rvalue reference to a
MyClass object.
This approach however is not so practical when the function has many arguments. On the code:
my_function(IC(a), IC(b), IC(c), IC(d));besides writing four times the IC function, the printed output will be split in four
distinct lines. Something like:
ic| a: 1
ic| b: 2
ic| c: 3
ic| d: 4
Unfortunately, just wrapping all the four arguments in a single IC call will not work
too. The returned value will be a std:::tuple with (a, b, c, d) and the my_function
expects four arguments.
To work around that, there is the IC_A function. IC_A behaves exactly like the IC
function, but receives a callable
as its first argument, and will call it using all the next arguments, printing all of them
before that. That previous example code could be rewritten as:
IC_A(my_function, a, b, c, d);and this time it will print:
ic| a: 1, b: 2, c: 3, d: 4
The IC_A function will return the same value as returned by the callable. The code:
auto mc = std::make_unique<MyClass>();
auto r = IC_A(mc->my_function, a, b);behaves exactly the same as:
auto mc = std::make_unique<MyClass>();
auto r = mc->my_function(a, b);but will print the values of a and b.
The variant IC_FA behaves the same as the IC_A function, but accepts an output
formatting string as its first argument, even before the callable
argument.
It is possible to configure how the value must be formatted while printing. The following code:
auto a = int{42};
auto b = int{20};
IC_F("#X", a, b);will print:
ic| a: 0X2A, b: 0X14
when using the IC_F variant instead of the plain IC functio. A
similar result would be obtained if using IC_FA and IC_FV in place of
IC_A and IC_V
respectively.
When using the formatting function variants (IC_F and IC_FA), the same formatting
string will be applied by default to all the arguments. That could be a problem if we wish
to have arguments with distinct formatting, or if the arguments have multiple types with
non mutually valid syntaxes. Therefore, to set a distinct formatting string to a specific
argument we can wrap it with the IC_ function. The code:
auto a = int{42};
auto b = int{20};
IC_F("#X", a, IC_("d", b));will print:
ic| a: 0X2A, b: 20
The IC_ function can be used within the plain IC (or IC_A) function too:
auto a = int{42};
auto b = int{20};
IC(IC_("#x", a), b);will print:
ic| a: 0x2a, b: 20
The last argument in an IC_ function call is the one that will be printed, all other
arguments that come before the last will be converted to a string using the
to_string function
and concatenated as the resulting formatting string.
auto a = float{1.234};
auto width = int{7};
IC(IC_("*<",width,".3", a));Will have as result a formatting string "*<7.3", and will print:
ic| a: 1.23***
Just for completeness in the examples, an usage of IC_FA and IC_FV would be:
IC_FA("#x", my_function, 10, 20);
auto rv0 = vws::iota(0) | IC_FV("[::2]:#x", "bar") | vws::take(5);This will print:
ic| 10: 0xa, 20: 0x14
and when iterating on rv0:
ic| bar[0]: 0
ic| bar[2]: 0x2
ic| bar[4]: 0x4
To IC_F and IC_FA, the syntax specification of the formatting strings depends both on
the type T being printed, and in that type's printing strategy
used by IceCream.
To IC_FV, the formatting syntax if the same as the Range format
string.
C strings are ambiguous. Should a char* foo variable be interpreted as a pointer to a
single char or as a null-terminated string? Likewise, is the char bar[] variable an
array of single characters or a null-terminated string? Is char baz[3] an array with
three single characters or is it a string of size two plus a '\0'?
Each one of those interpretations of foo, bar, and baz would be printed in a
distinct way. To the code:
char flavor[] = "pistachio";
IC(flavor);all three outputs below are correct, each one having a distinct interpretation of what
should be the flavor variable.
ic| flavor: 0x55587b6f5410
ic| flavor: ['p', 'i', 's', 't', 'a', 'c', 'h', 'i', 'o', '\u{0}']
ic| flavor: "pistachio"
A bounded char array (i.e.: array with a known size) will either be interpreted as an
array of single characters or let decay to a char*, subject to the
decay_char_array option.
An unbounded char[] arrays (i.e.: array with an unknown size) will decay to char*
pointers, and a character pointer will be printed either as a string or as a pointer as
configured by the show_c_string option.
The exact same logic as above applies to C strings of all character types, namely char,
wchar_t, char8_t, char16_t, and char32_t.
Character encoding in C++ is messy.
The char8_t, char16_t, and char32_t strings are well defined. They are capable, and
do hold Unicode code units of 8, 16, and 32 bits respectively, and they are encoded in
UTF-8, UTF-16, and UTF-32 also respectively.
The char strings have a well defined code unit bit size (given by
CHAR_BIT, usually 8 bits), but there
are no requirements about its encoding.
The wchar_t strings have neither a well defined code unit
size, nor any
requirements about its encoding.
In a code like this:
auto const str = std::string{"foo"};
std::cout << str;We will have three character encoding points of interest. In the first one, before
compiling, that code will be in a source file in an unspecified "source encoding". In the
second interest point, the compiled binary will have the "foo" string saved in an
unspecified "execution encoding". Finally on the third point, the "foo" byte stream
received by std::cout will be ultimately forwarded to the system, that expects the
stream being encoded in an also unspecified "output encoding".
From that three interest points of character encoding, both "execution encoding", and "output encoding" have impact in the inner working of Icecream-cpp, and there is no way to know for sure what is the used encoding in both of them. In face of this uncertainty, the adopted strategy is offer a reasonable default transcoding function, that will try convert the data to the right encoding, and allow the user to use its own implementation when needed.
Except for wide and Unicode string types (discussed below), when printing any other type we will have its serialized textual data in "execution encoding". That "execution encoding" may or may not be the same as the "output encoding", this one being the encoding expected by the configured output. Because of that, before we send that data to the output, we must transcode it to make sure that we have it in "output encoding". To that end, before delivering the text data to the output, we send it to the configured output_transcoder function, that must ensure it is encoded in the correct "output encoding".
When printing the wide and Unicode string types, we need to have one more transcoding level, because it is possible that the text data is in a distinct character encoding from the expected "execution encoding". Because of that, additional logic is applied to make sure that the strings are in "execution encoding" before we send them to output. This is further discussed in wide strings, and unicode strings sections.
The Icecream-cpp configuration system works "layered by scope". At the basis level we have
the global IC_CONFIG object. That global instance is shared by the whole running
program, as would be expected of a global variable. It is created with all config options
at its default values, and any change is readily seen by the whole program.
At any point of the code we can create a new config layer at the current scope by
instantiating a new IC_CONFIG variable, calling the IC_CONFIG_SCOPE() macro. All the
config options of this new instance will be in an "unset" state by default, and any
request to an option value not yet set will be delegated to its parent. That request will
go up on the parent chain until the first one having that option set answers.
All config options are set by using accessor methods of the IC_CONFIG object, and they
can be chained:
IC_CONFIG
.prefix("ic: ")
.show_c_string(false)
.line_wrap_width(70);IC_CONFIG is just a regular variable with a funny name to make a collision extremely
unlikely. When calling any IC*(...) macro, it will pick the IC_CONFIG instance at
scope by doing an unqualified name
lookup, using the same
rules applied to any other regular variable.
To summarize all the above, in the code:
auto my_function() -> void
{
IC_CONFIG.line_wrap_width(20);
IC_CONFIG_SCOPE();
IC_CONFIG.context_delimiter("|");
IC_CONFIG.show_c_string(true);
{
IC_CONFIG_SCOPE();
IC_CONFIG.show_c_string(false);
// A
}
// B
}At line A, the value of IC_CONFIG's line_wrap_width, context_delimiter, and
show_c_string will be respectively: 20, "|", and false.
After the closing of the innermost scope block, at line B, the value of IC_CONFIG's
line_wrap_width, context_delimiter, and show_c_string will be respectively: 20,
"|", and true.
The reading and writing operations on IC_CONFIG objects are thread safe.
Note
Any modification in an IC_CONFIG, other than to the global instance, will be seen only
within the current scope. As consequence, those modifications won't propagate to the
scope of any called function.
Enable or disable the output of IC(...) macro, enabled default.
- get:
auto is_enabled() const -> bool;
- set:
auto enable() -> Config&; auto disable() -> Config&;
The code:
IC(1);
IC_CONFIG.disable();
IC(2);
IC_CONFIG.enable();
IC(3);will print:
ic| 1: 1
ic| 3: 3
Sets where the serialized textual data will be printed. By default that data will be
printed on the standard error output, the same as std::cerr.
- set:
template <typename T> auto output(T&& t) -> Config&;
Where the type T must be one of:
- A class inheriting from
std::ostream. - A class having a method
push_back(char). - An output iterator that accepts the operation
*it = 'c'
For instance, the code:
auto str = std::string{};
IC_CONFIG.output(str);
IC(1, 2);Will print the output "ic| 1: 1, 2: 2\n" on the str string.
Warning
Icecream-cpp won't take ownership of the argument t, so care must be taken by the user
to ensure that it is alive.
A function that generate the text that will be printed before each output.
- set:
template <typename... Ts> auto prefix(Ts&& ...values) -> Config&;
Where each one of the types Ts must be one of:
- A string,
- A callable
T() -> U, whereUhas an overload ofoperator<<(ostream&, U).
The printed prefix will be a concatenation of all those elements.
The code:
IC_CONFIG.prefix("icecream| ");
IC(1);
IC_CONFIG.prefix([]{return 42;}, "- ");
IC(2);
IC_CONFIG.prefix("thread ", std::this_thread::get_id, " | ");
IC(3);will print:
icecream| 1: 1
42- 2: 2
thread 1 | 3: 3
Controls if a character pointer variable (char* wchar_t*, char8_t*, char16_t*, or
char32_t*) should be interpreted as a null-terminated C string (true) or a pointer to
a char (false). The default value is true.
- get:
auto show_c_string() const -> bool;
- set:
auto show_c_string(bool value) -> Config&;
The code:
char const* flavor = "mango";
IC_CONFIG.show_c_string(true);
IC(flavor);
IC_CONFIG.show_c_string(false);
IC(flavor);will print:
ic| flavor: "mango";
ic| flavor: 0x55587b6f5410
Controls if a character array variable (char[N] wchar_t[N], char8_t[N],
char16_t[N], or char32_t[N]) should decay to a character pointer (when true) to be
printed by the strings strategy (subject to the
show_c_string configuration), or remain as an array (when false) to
be printed by the range types strategy.
The default value is false.
- get:
auto decay_char_array() const -> bool;
- set:
auto decay_char_array(bool value) -> Config&;
The code:
char flavor[] = "caju";
IC_CONFIG.decay_char_array(true);
IC(flavor);
IC_CONFIG.decay_char_array(false);
IC(flavor);will print:
ic| flavor: "caju";
ic| flavor: ['c', 'a', 'j', 'u', '\u{0}']
Controls if a range type T will be printed using the range type strategy
even when the Formatting or
{fmt} libraries would be able to print it. We force the use of range
type strategy here because it supports more useful formatting options that would be
available otherwise if using some baseline strategy.
This option has a default value of true.
- get:
auto force_range_strategy() const -> bool;
- set:
auto force_range_strategy(bool value) -> Config&;
Controls if a tuple like type T will be printed using the tuple like
types strategy even when the
Formatting or {fmt}
libraries would be able to print it. We force the use of tuple like types strategy here
because it supports more useful formatting options that would be available otherwise if
using some baseline strategy.
This option has a default value of true.
- get:
auto force_tuple_strategy() const -> bool;
- set:
auto force_tuple_strategy(bool value) -> Config&;
Controls if a variant type T (either
std::variant or
boost::variant2::variant)
will be printed using the variant types strategy even when some of the
baseline strategies would be able to print it. We force the use of variant types
strategy here because it supports more useful formatting options that would be available
otherwise if using some baseline strategy.
This option has a default value of true.
- get:
auto force_variant_strategy() const -> bool;
- set:
auto force_variant_strategy(bool value) -> Config&;
Function that transcodes a wchar_t string, from a system defined encoding to a char
string in the system "execution encoding".
- set:
auto wide_string_transcoder(std::function<std::string(wchar_t const*, std::size_t)> transcoder) -> Config&; auto wide_string_transcoder(std::function<std::string(std::wstring_view)> transcoder) -> Config&;
There is no guarantee that the input string will end on a null terminator (this is the actual semantic of string_view), so the user must observe the input string size value.
The default implementation will check if the C locale is set to other value than "C" or
"POSIX". If yes, it will forward the input to the
std::wcrtomb function.
Otherwise, it will assume that the input is Unicode encoded (UTF-16 or UTF-32, accordingly
to the byte size of wchar_t), and transcoded it to UTF-8.
Function that transcodes a char32_t string, from a UTF-32 encoding to a char string in
the system "execution encoding".
- set:
auto unicode_transcoder(std::function<std::string(char32_t const*, std::size_t)> transcoder) -> Config&; auto unicode_transcoder(std::function<std::string(std::u32string_view)> transcoder) -> Config&;
There is no guarantee that the input string will end on a null terminator (this is the actual semantic of string_view), so the user must observe the input string size value.
The default implementation will check the C locale is set to other value than "C" or "POSIX". If yes, it will forward the input to the std::c32rtomb function. Otherwise, it will just transcoded it to UTF-8.
This function will be used to transcode all the char8_t, char16_t, and char32_t
strings. When transcoding char8_t and char16_t strings, they will be first converted
to a char32_t string, before being sent as input to this function.
Function that transcodes a char string, from the system "execution encoding" to a char
string in the system "output encoding", as expected by the configured output.
- set:
auto output_transcoder(std::function<std::string(char const*, std::size_t)> transcoder) -> Config&; auto output_transcoder(std::function<std::string(std::string_view)> transcoder) -> Config&;
There is no guarantee that the input string will end on a null terminator (this is the actual semantic of string_view), so the user must observe the input string size value.
The default implementation assumes that the "execution encoding" is the same as the "output encoding", and will just return an unchanged input.
The maximum number of characters before the output be broken on multiple lines. Default
value of 70.
- get:
auto line_wrap_width() const -> std::size_t;
- set:
auto line_wrap_width(std::size_t value) -> Config&;
If the context (source name, line number, and function name) should be printed even when
printing variables. Default value is false.
- get:
auto include_context() const -> bool;
- set:
auto include_context(bool value) -> Config&;
The string separating the context text from the variables values. Default value is "- ".
- get:
auto context_delimiter() const -> std::string;
- set:
auto context_delimiter(std::string const& value) -> Config&;
In order to be printable, a type T must satisfy at least one of the strategies described
in the next sections. If a type T is not printable, it can be mended by adding support
to one of the "baseline strategies": IOStreams, Formatting
library, and {fmt}.
If it happens that multiple strategies are simultaneously satisfied, the one with the higher precedence will be chosen. Within the "baseline strategies", the precedence order is: {fmt}, Formatting library, and IOStreams. The precedence criteria other than these are discussed in each strategy section.
Uses the STL IOStream library to print values. A
type T is eligible to this strategy if there exist a function overload
operator<<(ostream&, <SOME_TYPE>), where a
value of type T is accepted as <SOME_TYPE>.
Within the "baseline strategies" the IOStreams has the lowest precedence. So if a type is supported either by {fmt} or Formatting library they will be used instead.
The format string of IOStreams strategy is strongly based on the ones of STL Formatting and {fmt}.
It has the following specification:
format_spec ::= [[fill]align][sign]["#"][width]["." precision][type]
fill ::= <a character>
align ::= "<" | ">" | "^"
sign ::= "+" | "-"
width ::= integer
precision ::= integer
type ::= "a" | "A" | "b" | "B" | "c" | "d" | "e" | "E" | "f" | "F" | "g" | "G" | "o" | "s" | "x" | "X" | "?"
integer ::= digit+
digit ::= "0"..."9"
The fill character can be any char. The presence of a fill character is signaled by the character following it, which must be one of the alignment options. The meaning of the alignment options is as follows:
| Symbol | Meaning |
|---|---|
'<' |
Left align within the available space. |
'>' |
Right align within the available space. This is the default. |
'^' |
Internally align the data, with the fill character being placed between the digits and either the base or sign. Applies to integer and floating-point. |
Note that unless a minimum field width is defined, the field width will always be the same size as the data to fill it, so that the alignment option has no meaning in this case.
The sign option is only valid for number types, and can be one of the following:
| Symbol | Meaning |
|---|---|
'+' |
A sign will be used for both nonnegative as well as negative numbers. |
'-' |
A sign will be used only for negative numbers. This is the default. |
Causes the “alternate form” to be used for the conversion. The alternate form is defined differently for different types. This option is only valid for integer and floating-point types. For integers, when binary, octal, or hexadecimal output is used, this option adds the prefix respective "0b" ("0B"), "0", or "0x" ("0X") to the output value. Whether the prefix is lower-case or upper-case is determined by the case of the type specifier, for example, the prefix "0x" is used for the type 'x' and "0X" is used for 'X'. For floating-point numbers the alternate form causes the result of the conversion to always contain a decimal-point character, even if no digits follow it. Normally, a decimal-point character appears in the result of these conversions only if a digit follows it. In addition, for 'g' and 'G' conversions, trailing zeros are not removed from the result.
A decimal integer defining the minimum field width. If not specified, then the field width will be determined by the content.
The precision is a decimal number indicating how many digits should be displayed after the decimal point for a floating-point value formatted with 'f' and 'F', or before and after the decimal point for a floating-point value formatted with 'g' or 'G'. For non-number types the field indicates the maximum field size - in other words, how many characters will be used from the field content. The precision is not allowed for integer, character, Boolean, and pointer values. Note that a C string must be null-terminated even if precision is specified.
Determines how the data should be presented.
The available string presentation types are:
| Symbol | Meaning |
|---|---|
's' |
String format. |
'?' |
Debug format. The string is quoted and special characters escaped. |
| none | The same as '?'. |
The available character presentation types are:
| Symbol | Meaning |
|---|---|
'c' |
Character format. |
'?' |
Debug format. The character is quoted and special characters escaped. |
| none | The same as '?'. |
The available integer presentation types are:
| Symbol | Meaning |
|---|---|
'b' |
Binary format. Outputs the number in base 2. Using the '#' option with this type adds the prefix "0b" to the output value. |
'B' |
Binary format. Outputs the number in base 2. Using the '#' option with this type adds the prefix "0B" to the output value. |
'c' |
Character format. Outputs the number as a character. |
'd' |
Decimal integer. Outputs the number in base 10. |
'o' |
Octal format. Outputs the number in base 8. |
'x' |
Hex format. Outputs the number in base 16, using lower-case letters for the digits above 9. Using the '#' option with this type adds the prefix "0x" to the output value. |
'X' |
Hex format. Outputs the number in base 16, using upper-case letters for the digits above 9. Using the '#' option with this type adds the prefix "0X" to the output value. |
Integer presentation types can also be used with character and boolean values with the only exception that 'c' cannot be used with bool. Boolean values are formatted using textual representation, either true or false, if the presentation type is not specified.
The available presentation types for floating-point values are:
| Symbol | Meaning |
|---|---|
'a' |
Hexadecimal floating point format. Prints the number in base 16 with prefix "0x" and lower-case letters for digits above 9. Uses 'p' to indicate the exponent. |
'A' |
Same as 'a' except it uses upper-case letters for the prefix, digits above 9 and to indicate the exponent. |
'e' |
Exponent notation. Prints the number in scientific notation using the letter ‘e’ to indicate the exponent. |
'E' |
Exponent notation. Same as 'e' except it uses an upper-case 'E' as the separator character. |
'f' |
Fixed point. Displays the number as a fixed-point number. |
'F' |
Fixed point. Same as 'f', but converts nan to NAN and inf to INF. |
'g' |
General format. For a given precision p >= 1, this rounds the number to p significant digits and then formats the result in either fixed-point format or in scientific notation, depending on its magnitude. A precision of 0 is treated as equivalent to a precision of 1. |
'G' |
General format. Same as 'g' except switches to 'E' if the number gets too large. The representations of infinity and NaN are uppercased, too. |
Uses the STL formatting library to
print values. A type T is eligible to this strategy if there exist a struct
specialization
std::formatter<T>.
Within the "baseline strategies" the {fmt} has precedence over Formatting library, so if a type is supported by both, the {fmt} will be used instead.
The format string is forwarded to the STL Formatting library. Its syntax can be checked here.
Uses the {fmt} library to print values. A type T is eligible to this
strategy if there exist either a struct specialization
fmt::formatter<T> or a
function overload auto format_as(T).
{fmt} is a third-party library, so it needs to be available at the system and enabled to be supported by Icecream-cpp. An explanation of this is in the "third-party libraries" section.
The format string is forwarded to the {fmt} library. Its syntax can be checked here.
All character types: char, wchar_t, char8_t, char16_t, and char32_t. This
strategy will transcode any other character type to a char, using
either wide_string_transcoder or
unicode_transcoder as appropriated, and after that it will delegate
the actual printing to the IOStreams strategy.
This strategy has higher precedence than all the "baseline strategies".
The same as the IOStreams format string.
C strings (with some subtleties), STL's
strings, and STL's
string_views. These three
classes instantiated to all character types: char, wchar_t, char8_t, char16_t, and
char32_t.
This strategy will transcode any other character type to a char,
using either wide_string_transcoder or
unicode_transcoder as appropriated, and after that it will delegate
the actual printing to the IOStreams strategy.
This strategy has higher precedence than all the "baseline strategies".
The same as the IOStreams format string.
The std::unique_ptr<T> (before C++20) and boost::scoped_ptr<T> types will be printed
like usual raw pointers.
The std::weak_ptr<T> and boost::weak_ptr<T> types will print their address if they are
valid or "expired" otherwise. The code:
auto v0 = std::make_shared<int>(7);
auto v1 = std::weak_ptr<int> {v0};
IC(v1);
v0.reset();
IC(v1);will print:
ic| v1: 0x55bcbd840ec0
ic| v1: expired
This strategy has a lower precedence than the "baseline strategies". So if the printing type is supported by any one of them it will used instead.
Concisely, a range is any object of a type R, that holds a collection of elements and is
able to provide a [begin, end) pair, where begin is an iterator of type I and
end is a sentinel of type S. The iterator I is used to traverse the elements of R,
and the sentinel S is used to signal the end of the range interval, it may or may not be
the same type as I. In precise terms, the Icecream-cpp library is able to format a range
type R if it fulfills the
forward_range concept.
If a type R fulfills the range requirements and its elements are formattable by
IceCream, the type R is formattable by the range types strategy.
The code:
auto v0 = std::list<int>{10, 20, 30};
IC(v0);will print:
ic| v0: [10, 20, 30]
A view is close concept to ranges. Refer to the range views
pipeline section to see how to print them.
This strategy has a higher precedence than the "baseline strategies", so if the printing of a type is supported by both, this strategy will be used instead. This precedence can be disabled by the force_range_strategy configuration.
The accepted formatting string to a range type is a combination of both a range formatting and its elements formatting. The range formatting is syntactically and semantically almost identical to the Python slicing.
Formally, the accepted range types formatting string is:
format_spec ::= [range_fmt][":"elements_fmt]
range_fmt ::= "[" slicing | index "]"
slicing ::= [lower_bound] ":" [upper_bound] [ ":" [stride] ]
lower_bound ::= integer
upper_bound ::= integer
stride ::= integer
index ::= integer
integer ::= ["-"]digit+
digit ::= "0"..."9"
The same elements_fmt string will be used by all the printing elements, so it will have
the same syntax as the formatting string of the range elements.
The code:
auto arr = std::vector<int>{10, 11, 12, 13, 14, 15};
IC_F("[:2:-1]:#x", arr);will print:
ic| arr: [:2:-1]->[0xf, 0xe, 0xd]
Even though the specification says that lower_bound, upper_bound, stride, and
index, can have any integer value, some range capabilities can restrict them to just
positive values.
If a range is not sized, the
lower_bound, upper_bound, and index values must be positive. Similarly, if a range
is not bidirectional the
stride value must be positive too.
When printing within a range views pipeline using the IC_FV
function, all the lower_bound, upper_bound, and index values must be positive.
A std::pair<T1, T2> or std::tuple<Ts...> typed variables will print all of its
elements.
The code:
auto v0 = std::make_pair(10, 3.14);
auto v1 = std::make_tuple(7, 6.28, "bla");
IC(v0, v1);will print:
ic| v0: (10, 3.14), v1: (7, 6.28, "bla")
This strategy has a higher precedence than the "baseline strategies", so if the printing of a type supported by both, this strategy will be used instead. This precedence can be disabled by the force_tuple_strategy configuration.
The tuple like formatting specification is based on the syntax suggested in the Formatting Ranges paper. Since that part hasn't done to the proposal, with any future change we may revisit it here too.
tuple_spec ::= [casing][content]
casing ::= "n" | "m"
content ::= (delimiter element_fmt){N}
delimiter ::= <a character, the same to all N expansions>
element_fmt ::= <format specification of the element type>
Where the number N of repetitions in content rule is the tuple size.
The code:
auto v0 = std::make_tuple(20, "foo", 0.0123);
IC_F("n|#x||.3e", v0);will print:
ic| v0: 0x14, "foo", 1.230e-02
Controls the tuple enclosing characters and separator. If not used, the default behavior
is to enclose the values between "(" and ")", and separated by ", ".
If n is used, the tuple won't be enclosed by parentheses. If m is used the tuple will
be printed "map value like", i.e.: not enclosed by parentheses and using ": " as
separator. The m specifier is valid just to a pair or 2-tuple.
The formatting string of each tuple element, separated by a delimiter character. This
can be any character, which value will be defined by the fist read char when parsing
this rule.
Each element_fmt string will be forwarded to the respective tuple element when printing
it, so it must follow the formatting specification of that particular element type.
A std::optional<T> typed variable will print its value, if it has one, or nullopt
otherwise.
The code:
auto v0 = std::optional<int> {10};
auto v1 = std::optional<int> {};
IC(v0, v1);will print:
ic| v0: 10, v1: nullopt
This strategy has a lower precedence than the "baseline strategies". So if the printing type is supported by any one of them it will used instead.
optional_spec ::= [":"element_fmt]
element_fmt ::= <format specification of the element type>
auto v0 = std::optional<int>{50};
IC_F(":#x", v0);will print:
ic| v0: 0x32
A std::variant<Ts...> or boost::variant2::variant<Ts...> typed variable will print its
value.
The code:
auto v0 = std::variant<int, double, char> {4.2};
IC(v0);will print:
ic| v0: 4.2
This strategy has a higher precedence than the "baseline strategies", so if the printing of a type supported by both, this strategy will be used instead. This precedence can be disabled by the force_variant_strategy configuration.
variant_spec ::= [content]
content ::= (delimiter element_fmt){N}
delimiter ::= <a character, the same to all N expansions>
element_fmt ::= <format specification of the element type>
Where the number N of repetitions in content rule is the number of types in the
variant.
The code:
auto v0 = std::variant<int, char const*>{50};
IC_F("|b|s", v0);will print:
ic| v0: 110010
Types inheriting from std::exception will print the return of std::exception::what()
method. If beyond that it inherits from boost::exception too, the response of
boost::diagnostic_information() will be also printed.
The code:
auto v0 = std::runtime_error("error description");
IC(v0);will print:
ic| v0: error description
This strategy has a lower precedence than the "baseline strategies". So if the printing type is supported by any one of them it will used instead.
If using Clang >= 15, a class will be printable even without an operator<<(ostream&, T) overload.
The code:
class S
{
public:
float f;
int ii[3];
};
S s = {3.14, {1,2,3}};
IC(s);will print:
ic| s: {f: 3.14, ii: [1, 2, 3]}
This strategy has a lower precedence than the "baseline strategies". So if the printing type is supported by any one of them it will used instead.
The Icecream-cpp doesn't have any required dependency on external libraries besides the C++ standard library. However, it optionally supports printing some types of Boost and Range-v3 libraries, as well as using the {fmt} library alongside the STL's IOStreams and formatting libraries.
None of these external libraries are necessary for Icecream-cpp to work properly, and no action is required if anyone of them is not available.
All of the supported Boost types are forward declared in Icecream-cpp header, so you can print them with no further work, just like all the STL types.
Icecream-cpp can optionally support the printing of Range-v3 views, at any point of a pipeline flow. This functionality is fully described at the "range views pipeline" section.
The support to printing Range-v3 types can be explicitly enabled by defining the
ICECREAM_RANGE_V3 macro before the icecream.hpp header inclusion. That will work
either by explicitly defining it:
#define ICECREAM_RANGE_V3
#include "icecream.hpp"or by using a compiler command line argument if available. In GCC for example:
gcc -DICECREAM_RANGE_V3 source.cppEven when not explicitly defining the ICECREAM_RANGE_V3 macro, if the inclusion of the
icecream.hpp header is placed some lines below the inclusion of any Range-v3 header, it
will be automatically detected and the support enabled. So, a code like this will work
fine too:
#include <range/v3/view/transform.hpp>
#include "icecream.hpp"Icecream-cpp can optionally use the {fmt} library to get the string representation of a type. When available, the {fmt} library will take precedence over the STL's formatting and IOStreams libraries. A thorough explanation on this can be seen in the "baseline printable types" section.
The support to the {fmt} library can be explicitly enabled by defining the ICECREAM_FMT
macro before the icecream.hpp header inclusion. That will work either by explicitly
defining it:
#define ICECREAM_FMT
#include "icecream.hpp"or by using a compiler command line argument if available. In GCC for example:
gcc -DICECREAM_FMT source.cppEven when not explicitly defining the ICECREAM_FMT macro, if the inclusion of the
icecream.hpp header is placed some lines below the inclusion of any {fmt} header, it
will be automatically detected and the support enabled. So, a code like this will work
fine too:
#include <fmt/format.h>
#include "icecream.hpp"IC(...) is a preprocessor macro, it can cause conflicts if there is some
other IC identifier on code. To change the IC(...) macro to a longer ICECREAM(...)
one, just define ICECREAM_LONG_NAME before the inclusion of icecream.hpp header:
#define ICECREAM_LONG_NAME
#include "icecream.hpp"While most compilers will work just fine, until the C++20 the standard requires at least
one argument when calling a variadic macro. To handle this the nullary macros IC0() and
ICECREAM0() are defined alongside IC(...) and ICECREAM(...).