Additionally, using #include to include a standard header file within a declaration or definition, or using part of The Standard Library before the inclusion of the related standard header file leads to undefined behaviour.

Example

/* f.h */ 
xyz = 0;

/* f.c */

int16_t 
#include "f.h"            /* Non-compliant */

/* f1.c */ 
#define F1_MACRO

#include "f1.h"           /* Compliant     */ 
#include "f2.h"           /* Compliant     */

int32_t i = 0;

#include "f3.h"           /* Non-compliant */

MISRA-C 2004 Rule 19.1 (advisory): #include statements in a file should only be preceded by other preprocessor directives or comments.

Include directive preceded by a preprocessor output token.

All the #include statements in a particular code file should be grouped together near the head of the file. The rule states that the only items which may precede a #include in a file are other preprocessor directives or comments.

MISRA-C++ 2008 Rule 16-0-1 (required): #include directives in a file shall only be preceded by other preprocessor directives or comments.

Rationale

To aid code readability, all the #include directives in a particular code file should be grouped together near the head of the file. The only items which may precede a #include in a file are other preprocessor directives or comments.

Example

#include <f1.h>  // Compliant

int32_t i;

#include <f2.h>  // Non-compliant