Why is this an issue?
The standard C library includes a number of functions for handling streams. If not called correctly, these functions can have undefined behavior.
More specifically:
-
FILE* should be checked for null before being used in a function that accesses the file content
- The third argument of
fseek must be SEEK_SET, SEEK_END, or SEEK_CUR
Noncompliant code example
FILE *file1 = fopen("myFile", "r");
fseek(file1, 1, SEEK_SET); // Noncompliant, file could be NULL
fclose(file1);
FILE *file2 = tmpfile();
ftell(file2); // Noncompliant, file could be NULL
if (file2) {
fseek(file2, 1, 3); // Noncompliant, third argument should either be SEEK_SET, SEEK_CUR or SEEK_END
}
fclose(file2);
Compliant solution
FILE *file1 = fopen("myFile", "r");
if (file1) {
fseek(file1, 1, SEEK_SET);
fclose(file1);
}
FILE *file2 = tmpfile();
if (file2) {
ftell(file2);
fseek(file2, 1, SEEK_END);
fclose(file2);
}
