Implicit declaration of function 'fopen_s' is invalid in C99

Asked Oct 05 '20 at 20:58

Active Oct 05 '20 at 20:58

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I am writing a function in C for class and we were given this as a starter to the assignment. I have literally copied and pasted however I am gettin and error that reads "Implicit declaration of function 'fopen_s' is invalid in C99" and "Use of undeclared identifier 'fp'"

#include <stdio.h>

int compare(void);

int main(void) {
int i;

fopen_s(&fp, "largeSmallLab.txt", "w");

for (i = 1; i <= 4; ++i) {
    compare();
}

fclose(fp);
return 0;

}

asked Oct 05 '20 at 20:58

sinafarheidar12

1

`fopen_s` is Windows stuff, are you compiling with Visual Studio? Otherwise the compiler is complaining about a non existing function and in this case you should use plain `fopen`. – David Ranieri Oct 05 '20 at 21:00
1

`_s` functions are an optional part of the C99 standard. Generally only Microsoft compilers implement them. – n. m. could be an AI Oct 05 '20 at 21:01
No I am running this on Mac (XCode) – sinafarheidar12 Oct 05 '20 at 21:01
So i can just run fopen() like normal? – sinafarheidar12 Oct 05 '20 at 21:02
1

@sinafarheidar12 of course, you can use `fopen`, but always check his result. – David Ranieri Oct 05 '20 at 21:02

Implicit declaration of function 'fopen_s' is invalid in C99

0 Answers0