The C Standard defines a set of predefined macros (see subclause 6.10.8) to help the user determine if the BB. Definitions#implementation implementation being used is a BB. Definitions#conforming conforming implementation, and if so, to which version of the C Standard it conforms. These macros can also help the user to determine which of the standard features are implemented.
The following tables list these macros and indicate in which version of the C Standard they were introduced. The following macros are required:
| 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:
| Macro Name | C90 | C99 | C11 |
|---|---|---|---|
|
✓ | ✓ | |
|
✓ | ✓ | ||
|
✓ | ||
|
✓ |
The following are optional feature macros:
| Macro Name | C90 | C99 | C11 |
|---|---|---|---|
|
✓ | |||
|
✓ | ✓ | |
|
✓ | ✓ | ||
|
| ✓ | ||
|
✓ | ||
|
✓ | ||
|
✓ | |||
|
| ✓ |
The following is optional and is defined by the user:
| Macro Name | C90 | C99 | C11 |
|---|---|---|---|
__STDC_WANT_LIB_EXT1__ |
| ✓ |
Noncompliant Code Example (Checking Value of Predefined Macro)
...
| 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)
...
| 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)
...
| 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_tMSC14-C. Do not introduce unnecessary platform dependencies)
| 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;
}
|
Compliant Solution (Optional Language Features)
...
| 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>
#if !defined(USE_EXT1)
#include "safe_str_lib.h"
#endif
int main(void) {
char source_msg[] = "This is a test.";
char *msg = malloc(sizeof(source_msg) + 1);
if (msg != NULL) {
strcpy_s(msg, sizeof msg, source_msg);
}
else {
return EXIT_FAILURE;
}
return 0;
}
|
Risk Assessment
Not testing for language features or the version of the BB. Definitions#implementation implementation being used can lead to unexpected or BB. Definitions#undefined undefined program behavior.
Rule | Severity | Likelihood | Remediation Cost | Priority | Level |
|---|---|---|---|---|---|
PRE13-C | Low | Probable | Low | P6 | L2 |
Automated Detection
Tool | Version | Checker | Description | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Axivion Bauhaus Suite |
| CertC-PRE13 | |||||||
| LDRA tool suite |
| Partially implemented |
Related Vulnerabilities
Search for BB. Definitions#vulnerability 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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