The C Standard defines a set of predefined macros (see subclause 6.10.8) to help the user determine if the implementation BB. Definitions#implementation being used is a conforming BB. Definitions#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.
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| 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;
}
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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 implementation BB. Definitions#implementation being used can lead to unexpected or undefined program BB. Definitions#undefined behavior.
Rule | Severity | Likelihood | Remediation Cost | Priority | Level |
|---|---|---|---|---|---|
PRE13-C | Low | Probable | Low | P6 | L2 |
Related Vulnerabilities
Search for vulnerabilities BB. Definitions#vulnerability resulting from the violation of this rule on the CERT website.
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| 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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