Does't work fopen_s(&file, "filename", mode) in visual studio 2019 C_language

user_15447310 0
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So this is my first question here. If you could help me, that would be much appreciated. This code is about my thesis. I'm trying to write to a file and it works but trying to read another file is not reading. I can't make it work. "file does not open" appears on the screen. Help me please, for read to file.

#include <cstdio>
#include <stdlib.h>
#include <stdio.h>
#include <time.h>

int main()
{
    FILE* myfile;
    errno_t errorcode = fopen_s(&myfile, "output.txt", "w");

    if (myfile == NULL)
    {
       printf("Error");
    }

    FILE* data; 
    errno_t err = fopen_s(&data, "C:\SA\input.txt", "r");

    //errno_t err = fopen_s(&data, "input.txt", "r");

    if(data==NULL)
    {
       printf("file does not open");
    }
return 0;
getchar();
}
visual-studio-2019 visual-studio c c++
1 Answers

The original code posted had 2 major issues:

  • "C:\SA\input.txt" should be "C:\\SA\\input.txt" or simply "C:/SA/input.txt". Microsoft's legacy systems use \ as a path separator which must be escaped in C strings as \\ (and in many other languages too). The traditional path separator on POSIX systems is / and it is also supported in Windows.
  • if(data==NULL); is a test with an empty statement, hence nothing happens.
  • Note that you should not use C++ headers such as <iostream> in a C program.

Here is a simplified version:

#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main() {
    FILE *myfile;
    errno_t err = fopen_s(&myfile, "output.txt", "w");
    if (err) {
        fprintf(stderr, "Cannot open file %s: %s\n",
                "output.txt", strerror(err));
        return 1;
    }

    FILE *data; 
    err = fopen_s(&data, "C:\\SA\\input.txt", "r");
    if (err) {
        fprintf(stderr, "Cannot open file %s: %s\n",
                "C:\\SA\\input.txt.txt", strerror(err));
        return 1;
    }
    getchar();  // keep terminal window open
    return 0;
}
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