feature_test_macros - Linux

Overview

The feature_test_macros command is utilized during the compilation stage of a C or C++ program to ascertain whether specific language features are supported by the compiler. It enables developers to test for the availability of specific features and conditionally compile code based on the results.

Syntax

#include <features.h>

#define __STDC_VERSION__  199410L
#define __STDC_HOSTED__  1
#define __cplusplus  199711L
#define __linux  1
#define __unix  1
#define __unix__  1
#define __USE_POSIX  1
#define __USE_POSIX2  1
#define __USE_POSIX199309  1
#define __USE_POSIX199506  1
#define __USE_XOPEN  1
#define __USE_XOPEN2K  1
#define __USE_XOPEN2K8  1
#define __USE_XOPEN_EXTENDED  1
#define __USE_GNU  1
#define __USE_SVID  1
#define __USE_BSD  1
#define __USE_MISC  1
#define __USE_ISOC11  1
#define __USE_ISOC99  1
#define __USE_ISOC2X  1
#define __USE_ISOC1X  1
#define __USE_ISOC95  1
#define __USE_ISOC199506  1
#define __USE_POSIX_IMPLICITLY  1
#define __USE_POSIX2_IMPLICITLY  1
#define __USE_POSIX199309_IMPLICITLY  1
#define __USE_POSIX199506_IMPLICITLY  1
#define __USE_XOPEN2K8_IMPLICITLY  1
#define __USE_XOPEN2K_IMPLICITLY  1
#define __USE_XOPEN_EXTENDED_IMPLICITLY  1
#define __USE_BSD_IMPLICITLY  1
#define __USE_MISC_IMPLICITLY  1
#define __USE_ISOC11_IMPLICITLY  1
#define __USE_ISOC99_IMPLICITLY  1
#define __USE_ISOC2X_IMPLICITLY  1
#define __USE_ISOC1X_IMPLICITLY  1
#define __USE_ISOC95_IMPLICITLY  1
#define __USE_ISOC199506_IMPLICITLY  1
#define __STDC_ISO_10646__  201706L
#define __WORDSIZE  64
#define __BYTE_ORDER  __LITTLE_ENDIAN
#define __ORDER_BIG_ENDIAN__  4321
#define __ORDER_LITTLE_ENDIAN__  1234
#define __ORDER_PDP_ENDIAN__  3412
#define __FLOAT_WORD_ORDER  __ORDER_LITTLE_ENDIAN__
#define __SIZEOF_INT__  4
#define __SIZEOF_LONG__  8
#define __SIZEOF_LONG_LONG__  8
#define __SIZEOF_SHORT__  2
#define __SIZEOF_FLOAT__  4
#define __SIZEOF_DOUBLE__  8
#define __SIZEOF_LONG_DOUBLE__  16
#define __SIZEOF_SIZE_T__  8
#define __SIZEOF_WCHAR_T__  4
#define __SIZEOF_WINT_T__  4
#define __SIZEOF_POINTER__  8
#define __SIZE_TYPE__  long int
#define __PTRDIFF_TYPE__  long int
#define __WCHAR_TYPE__  int
#define __WINT_TYPE__  int
#define __INTPTR_TYPE__  long int
#define __UINTPTR_TYPE__  long unsigned int

Options/Flags

This command does not have any options or flags.

Examples

C Example:

#include <stdio.h>
#include <features.h>

int main() {
  #if __STDC_VERSION__ >= 199901L
    printf("C99 standard is supported.\n");
  #else
    printf("C99 standard is not supported.\n");
  #endif

  return 0;
}

C++ Example:

#include <iostream>
#include <features.h>

int main() {
  #if __cplusplus >= 201103L
    std::cout << "C++11 standard is supported." << std::endl;
  #else
    std::cout << "C++11 standard is not supported." << std::endl;
  #endif

  return 0;
}

Common Issues

Incorrect C/C++ Version Check: Ensure that you are using the correct version macro for feature testing. The version macros, such as __STDC_VERSION__ and __cplusplus, indicate the supported version of the C or C++ standard, not the version of the compiler itself.
Missing <features.h> Header: Remember to include the <features.h> header in your code to access the feature test macros.

Integration

Feature test macros can be combined with conditional compilation to selectively enable or disable code blocks based on the availability of specific features. This allows for cross-platform code development and ensures that the code executes correctly on systems with varying levels of support for different language features.

Related Commands

cpp: C preprocessor that can perform macro expansion and conditional compilation.
gcc: GNU C compiler.
clang: LLVM C/C++/Objective-C compiler.