C中的VS2013文件打开错误

Question

i use a vs2013.

#include <stdio.h>

void main(){

    FILE *f;
    char fname[] = "17_1.txt";

    if ((f = fopen_s(f,fname, "r+")) == NULL)
    {
        fprintf(stdout, "can't open the file\n");
        exit(1);
    }
    while (!feof(f))
    {
        fscanf_s(f, "%d %s %d %d\n");
        fprintf(stdout, "%d %s %d %d \n");
    }

    fclose(f);
}

but Error 4 error C4700: uninitialized local variable 'f' used I saw-_- how must i change?

Answer 1

You seem to be confusing fopen_s and fopen . The signature of fopen_s is:

errno_t fopen_s( 
   FILE** pFile,
   const char *filename,
   const char *mode 
);

And the signature of fopen is:

FILE *fopen(const char *restrict filename, const char *restrict mode);

The way you use these two functions respectively is:

FILE* f = NULL;
errno_t e;

if ((e = fopen_s(&f, fname, "r+")) != 0)
{
    fprintf(stdout, "can't open the file\n");
}

and:

if ((f = fopen(fname, "r+")) == NULL)

If an error occurs, fopen sets errno .