PRE04-C. Do not reuse a standard header file name

If a file with the same name as a standard header is placed in the search path for included source files, the behavior is undefined .

The following table from the C Standard, subclause 7.1.2 [ ISO/IEC 9899:2011 ], lists these standard headers:

`<assert.h>`	`<float.h>`	`<math.h>`	`<stdatomic.h>`	`<stdlib.h>`	`<time.h>`
`<complex.h>`	`<inttypes.h>`	`<setjmp.h>`	`<stdbool.h>`	`<stdnoreturn.h>`	`<uchar.h>`
`<ctype.h>`	`<iso646.h>`	`<signal.h>`	`<stddef.h>`	`<string.h>`	`<wchar.h>`
`<errno.h>`	`<limits.h>`	`<stdalign.h>`	`<stdint.h>`	`<tgmath.h>`	`<wctype.h>`
`<fenv.h>`	`<locale.h>`	`<stdarg.h>`	`<stdio.h>`	`<threads.h>`

Do not reuse standard header file names, system-specific header file names, or other header file names.

Noncompliant Code Example

In this noncompliant code example, the programmer chooses to use a local version of the standard library but does not make the change clear:

#include "stdio.h"  /* Confusing, distinct from <stdio.h> */

/* ... */

The solution addresses the problem by giving the local library a unique name (per PRE08-C. Guarantee that header file names are unique ), which makes it apparent that the library used is not the original:

/* Using a local version of stdio.h */ 
#include "mystdio.h"

/* ... */

Using header file names that conflict with other header file names can result in an incorrect file being included.

Recommendation	Severity	Likelihood	Detectable	Repairable	Priority	Level
PRE04-C	Low	Unlikely	Yes	No	P2	L3

Tool	Version	Checker	Description
Axivion Suite	7.12.0	CertC-PRE04
Cppcheck Premium	24.11.0	premium-cert-pre04-c
ECLAIR	1.2	CC2.PRE04	Fully implemented
Helix QAC	2025.2	C5001
LDRA tool suite	9.7.1	568 S	Fully implemented
Polyspace Bug Finder	R2025b	CERT C: Rec. PRE04-C	Checks for reuse of standard header file (rec. fully covered)
Security Reviewer - Static Reviewer	6.02	RTOS_22	Fully implemented

Search for vulnerabilities resulting from the violation of this rule on the CERT website .


CERT Oracle Secure Coding Standard for Java	DCL01-J. Do not reuse public identifiers from the Java Standard Library


[ ISO/IEC 9899:2011 ]	Subclause 7.1.2, "Standard Headers"