Summary
When using fgets(), I have error checking code that performs some remediation in case fgets() returns null but isn't yet at end of file. I'd like to exercise this section of code to verify it's working as intended.
Is there a canonical way to trigger fgets() to fail? Either through manual means (somehow deleting the file between calls to fgets()), some test setup (providing a knowingly "corrupt" file), or something else?
Minimally Reproducible Example
fgets_fail_test.cpp:
// Test code to show minimally reproducible example of fgets() error handling
// The desire is to manually trigger a failure in fgets()
#include <errno.h>
#include <iostream>
#include <stdio.h>
#include <string.h>
int main(int argc, char **argv) {
FILE *fp = fopen("test_file.txt", "r"); //assume this works, not testing this
char buf[100]; //assume large enough to hold data
unsigned int lineno = 1;
while (fgets(buf, 100, fp)) {
std::cout << buf;
lineno++;
}
if (feof(fp)) {
std::cout << "End of file encountered.\n";
}
else if (ferror(fp)) { // how do I trigger an fgets error to cause this to return true?
printf("Encountered read error at line no %u. Error: %d, %s.\n",
lineno,
errno,
strerror(errno));
}
fclose(fp); // assume this works, not testing this
return 0;
}
test_file.txt:
ABCDEFG
HIJKLMN
OPQRSTU
VWXYZ
The quick brown fox
jumped over the
lazy dog.
Goodbye.
Theories
While I could simply replace the code in question with some test scaffolding (write an fgets wrapper that keeps internal state, increment a counter, once it reaches line #N, it returns null and manually sets file error and errno) I feel like there should be some "builtin" way to do this?
If the only solution is scaffolding, I'll do that. Honestly maybe I'm trying to be too clever here.
