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The tables below list these macros and which version of the C Standard they were introduced. The following macros are required in C11.:

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 The following are optional environment macros in C11.:

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 The following are optional feature macros in C11.:

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 The following is optional in C11 and is defined by the user:

Noncompliant Code Example (Checking value of predefined macro)

The value a C Standard predefined macro macros should never be tested for a value before the macro is tested to make sure it is definedtested for definition, as shown in this noncompliant code example:

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In this compliant solution, the definition of the predefined macro __STDC__ is tested before the value of the macro is tested: 

#include <stdio.h>

int main(void) {
  #if defined(__STDC__)
    #if (__STDC__ == 1)
      printf("Implementation is ISO-conforming.\n");
    #else
      printf("Implementation is not ISO-conforming.\n");
    #endif
  #else   /* !defined(__STDC__) */
    printf("__STDC__ is not defined.\n");
  #endif
  /* ... */
  return 0;
}

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Compliant Solution (Test for Optional feature)

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