CODEWITHSUNDEEP
c
aMaNux
aMaNux

Reputation: 25

Pointers of FILE?

Currently learning the C programming language, I'd like to get in practice some of my knowledge in pointers and file writing. I chose so to write a little software, however, it does not write into the file, there is the the code below.

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

#define INIT_FAILED 0
#define INIT_SUCCESS 1

int init(char filename[], FILE* logFile);

int init(char filename[], FILE* logFile){

    FILE* fileToWrite = NULL;
    char dir[] = "logs\\";
    strcat(dir, filename);

    fileToWrite = fopen(dir, "w");

    if(fileToWrite!=NULL){

        \\ I think the error is on this line below, but I'm not able to determine why

        *logFile = *fileToWrite;
        return INIT_SUCCESS;

    } else{

        return INIT_FAILED;

    }   

}

int main(int argc, char* argv[]){

    char filename[] = "log";
    FILE* logFile = malloc(sizeof(FILE));

    if(logFile == NULL){
        return 0;
    }

    if(init(filename, logFile)){
        fputc('A', logFile)
    }
}

I would obviously take with pleasure every suggestions to a better readability of my code.

Thank you.

Upvotes: 1

Views: 195

Answers (3)

Weather Vane
Weather Vane

Reputation: 34585

I've made some corrections to the code, shown by comments. It's not necessary to allocate memory for a single pointer. You already need a pointer to a pointer as the function argument, so it just complicates things. This passes the address of the file pointer to the function, so it can set the variable in main.

Note that your string would overflow, I added some spare length, although this quick fix could be improved, perhaps with strncat.

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

#define INIT_FAILED 0
#define INIT_SUCCESS 1

int init(char filename[], FILE** logFile);

int init(char filename[], FILE** logFile){  // double star

    FILE* fileToWrite = NULL;
    char dir[100] = "log\\";                // enough length for strcat
    strcat(dir, filename);

    fileToWrite = fopen(dir, "w");
    if(fileToWrite!=NULL){
        *logFile = fileToWrite;             // remove *
        return INIT_SUCCESS;
    }

    return INIT_FAILED;
}

int main(int argc, char* argv[]){

    char filename[] = "log.txt";
    FILE* logFile;                          // remove memory allocation

    if(init(filename, &logFile)){           // pass address of the FILE* pointer
        fputc('A', logFile);                // ; was missing
        fclose(logFile);                    // tidy up
    }
}

Upvotes: 2

Dima Belemezov
Dima Belemezov

Reputation: 35

FILE* fileToWrite = fopen("yourfilename.txt", "wr/wb/eb/a...");
    if (fileToWrite==NULL){
        perror(NULL);
        exit(1);
    }

Upvotes: 0

0___________
0___________

Reputation: 67516

IMO you overcomplicate simple things. You do not have to return status as the status is your fopen result. 

FILE *init(const char filename[])
{
    /* ... */

    return fopen(dir, "w");
}

and then 

    if((logFile = init(filename))){
        fputc('A', logFile)
    }

Upvotes: 2

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