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Consider a multithreaded application that encounters an error while calling a system function. The strerror() function returns a human-readable error string given an error number. The C Standard, Section subclause 7.24.6.2 [ISO/IEC 9899:2011], specifically states that strerror() is not required to avoid data races. Conventionally, it could rely on a static array that maps error numbers to error strings, and that array might be accessible and modifiable by other threads.
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#include <errno.h>
#include <stdio.h>
#include <string.h>
void f(FILE *fp) {
fpos_t pos;
errno = 0;
if (0 != fgetpos(fp, &pos)) {
char *errmsg = strerror(errno);
printf("Could not get the file position because of %s\n",
errmsg);
}
} |
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#define __STDC_WANT_LIB_EXT1__ 1 #include <errno.h> #include <stdio.h> #include <string.h> enum { BUFFERSIZE = 64 }; void f(FILE *fp) { fpos_t pos; errno = 0; if (0 != fgetpos(fp, &pos)) { char errmsg[64BUFFERSIZE]; if (strerror_s(errmsg, sizeof(errmsg)BUFFERSIZE, errno) != 0) { /* Handle error */ } printf("Could not get the file position because of %s\n", errmsg); } } |
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#include <errno.h> #include <stdio.h> #include <string.h> enum { BUFFERSIZE = 64 }; void f(FILE *fp) { fpos_t pos; errno = 0; if (0 != fgetpos(fp, &pos)) { char errmsg[64BUFFERSIZE]; if (strerror_r(errno, errmsg, sizeof(errmsg)BUFFERSIZE) != 0) { /* Handle error */ } printf("Could not get the file position because of %s\n", errmsg); } } |
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| [Historical information about POSIX.1 Thread Safety] | Section 2.9.1 |
| [ISO/IEC 9899:2011] | Section Subclause 7.24.6.2, "The |
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