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| Macro Name | C90 | C99 | C11 |
|---|---|---|---|
| ✓ | ✓ | ✓ |
|
| ✓ | ✓ |
|
| ✓ | ✓ |
| ✓ | ✓ | ✓ |
| ✓ | ✓ | ✓ |
| ✓ | ✓ | ✓ |
| ✓ | ✓ | ✓ |
1) __STDC_VERSION__ was introduced by an Amendment to C90, this version of the C Standard is commonly call C94
The following are optional environment macros:
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| Macro Name | C90 | C99 | C11 |
|---|---|---|---|
__STDC_WANT_LIB_EXT1__ | ✓ |
Noncompliant Code Example (Checking Value of Predefined Macro)
C Standard predefined macros should never be tested for a value before the macro is tested for definition, as shown in this noncompliant code example:
| Code Block | ||||
|---|---|---|---|---|
| ||||
#include <stdio.h>
int main(void) {
#if (__STDC__ == 1)
printf("Implementation is ISO-conforming.\n");
#else
printf("Implementation is not ISO-conforming.\n");
#endif
/* ... */
return 0;
}
|
Compliant Solution (Testing for Definition of Macro)
In this compliant solution, the definition of the predefined macro __STDC__ is tested before the value of the macro is tested:
| Code Block | ||||
|---|---|---|---|---|
| ||||
#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;
} |
Compliant Solution (Test for Optional feature)
This compliant solution tests to see if the C11 predefined macro __STDC_ANALYZABLE__ is defined and what value the implementation has given the macro:
| Code Block | ||||
|---|---|---|---|---|
| ||||
#include <stdio.h>
int main(void) {
#if defined (__STDC__)
#if defined(__STDC_VERSION__) && (__STDC_VERSION__ >= 201112L) /* C11 */
#if defined(__STDC_ANALYZABLE__)
#if (__STDC_ANALYZABLE__ == 1)
printf("Compiler conforms to Annex L (Analyzability).\n");
#else
printf("Compiler does not support Annex L (Analyzability).\n");
#endif
#else
printf("__STDC_ANALYZABLE__ is not defined.\n");
#endif
#else
printf("Compiler not C11.\n");
#endif
#else
printf("Compiler not Standard C.\n");
#endif
return 0;
} |
Compliant Solution (Optional Language Features)
This compliant solution checks for the C11 optional language features in Annex K. If Annex K is supported by the implementation, the functions defined in Annex K are used; if Annex K is not supported, then the standard library functions are used. (See DCL09-C. Declare functions that return errno with a return type of errno_t.)
| Code Block | ||||
|---|---|---|---|---|
| ||||
#if defined(__STDC_LIB_EXT1__)
#if (__STDC_LIB_EXT1__ >= 201112L)
#define USE_EXT1 1
#define __STDC_WANT_LIB_EXT1__ 1 /* Want the ext1 functions */
#endif
#endif
#include <string.h>
#include <stdlib.h>
int main(void) {
char source_msg[] = "This is a test.";
char *msg = malloc(sizeof(source_msg) + 1);
if (msg != NULL) {
#if defined(USE_EXT1)
strcpy_s(msg, sizeof msg, source_msg);
#else
strcpy(msg, source_msg);
#endif
}
else {
return EXIT_FAILURE;
}
return 0;
}
|
Risk Assessment
Not testing for language features or the version of the implementation being used can lead to unexpected or undefined program behavior.
Rule | Severity | Likelihood | Remediation Cost | Priority | Level |
|---|---|---|---|---|---|
PRE13-C | Low | Probable | Low | P6 | L2 |
Related Vulnerabilities
Search for vulnerabilities resulting from the violation of this rule on the CERT website.
Related Guidelines
| ISO/IEC TR 24772:2013 | Pre-processor Directives [NMP] |
| [ISO/IEC 9899:2011] | 6.10.8, "Predefined macro names" K.3.7.1, "Copying functions" |
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