Receiving input from a stream directly following an output to that stream (or vice versa) without an intervening call to fflush(), fseek(), fsetpos(), or rewind() results in undefined behavior. Therefore, Consequently a call to one of these functions is necessary in between input and output to the same update stream.
Non-Compliant Code Example
...
| Code Block | ||
|---|---|---|
| ||
/* somelocation deviceto usedbe forread bothor inputwritten andto output */ const char *filename = "/dev/device2"; FILE *file = fopen(filename, "rb+"); if (file == NULL) { /* handle error */ } /* write to file stream */ /* read response from file stream */ fclose(file); |
...
| Code Block | ||
|---|---|---|
| ||
/*location someto devicebe usedread foror both input and outputwritten to */ const char *filename = "/dev/device2"; FILE *file = fopen(filename, "rb+"); if (file == NULL) { /* handle error */ ] /* write to file stream */ fflush(file); /* read response from file stream */ fclose(file); |
...