Not to bother anyone, but i have ran into an issue with a class of mine, somehow when i write to a file with the FILE* and fprintf() function i don't get any text in my text file that i created, i have searched all over youtube and i don't know what i'm doing wrong, because my code is the same.

Heres a copy of my .c and .h code:

main.c :

#include <iostream>

#include "../include/include.h"

using namespace std;

int main() {
    
    write_file wf("test.txt");
    wf.write_line("Hello, world!");

    return 0;
}

include.h:

#ifndef INCLUDE_H
#define INCLUDE_H

#include <iostream>

class write_file {
public:
    write_file(const char *file_name) {
        FILE* fp = fopen(file_name, "w");
    }
    void write_line(const char *line) {
        fprintf(fp, "%s\n", line);
    }
    void close() {
        fclose(fp);
    }
    private: FILE* fp;
};

#endif /* include.h */

CodePudding user response：

Main issue:

To fix your issue, you have to remove the local fp variable that shadows the class member.

When the compiler sees FILE *fp in your method, it uses a separate variable and is not referring to the one in your class instance.

Change the method definition to:

    write_file(const char *file_name) {
        fp = fopen(file_name, "w");
    }

Additional points I really ought to comment on:

• You never call close. Mishandling resources is one of the most common mistakes in C & CPP. Make sure to implement a destructor that calls close. If you do that, make sure to improve the close implementation to handle multiple calls.

• Consider using standard CPP classes for interacting with files, specifically ifstream and ofstream. Those handle a lot of the fuss automagically for you.

• Please don't use .c as a file extension. This is really odd. Most CPP developers use .cpp or .cc for CPP source files.

• I might be saying that because I'm not a gen-Z kid, but please don't search Youtube for programming tutorials. Searching text-based sources is so much more efficient. Learn how to use cplusplus or cppreference instead.