Ytukyg

my text file is "Foo bar!!", name foo.txt

So i want to create a new variable in my main function and copy the text file into new variable.

#include <stdio.h>

#include <stdlib.h>



FILE *fopen_with_error (const char *f, const char *mode){

    FILE *fp;

    if((fp = fopen(f,mode)) == NULL){

        printf("Error opening %sn",f);

        exit(EXIT_FAILURE);

    }

    return fp;

}



int main(int argc, char* argv){



    FILE *fp;

    int a, num;

    if(argc != 2){

        printf("Usage: program input filen");

        return 0;

    }

    fp = fopen_with_error(argv[1],"rb");

}

I want to store the copied text into 'a' variable.

I tried to use fread function but everytime i try, it fails somehow.

In addition to using stat to obtain the number of bytes in the file to accurately size your buffer for reading the file into a single variable, you can also use fseek and ftell to accomplish the same thing.

The bigger issue is that you post the contents of a text file with a single-line (e.g. "Foo bar!!") and then proceed to explain you want to read the entire file into a variable. For binary input, that makes more sense. For text, you generally want to read and store individual lines rather than a file-at-once.

(you can store an entire text file line-by-line by using a pointer to pointer to char and allocating pointer and then storage for each line)

Now, don't get me wrong, you can do either, but if you need specific information from each line, and the lines differ in length, etc.., it is a whole lot easier to iterate over pointers than it is trying to scan through one giant buffer of text picking out newlines. You can think through what you need to do with the data you read from the file and make the call.

As your question is written, the basic approach is simply to open the file in binary mode, fseek forward to the end of file, use ftell to report the number of bytes in the file, allocate/validate memory to hold the file, and then read the file using fread into the allocated block of memory. (note: mmap provides another option as well)

Putting that pieces together, you could do something like the following:

#include <stdio.h>

#include <stdlib.h>



char *read_file (char* fname, size_t *nbytes)

{

    long bytes = 0;

    char* file_content;

    FILE *file = fopen(fname, "rb");



    if (!file)          /* validate file open for reading */

        return NULL;



    fseek (file, 0, SEEK_END);              /* fseek end of file */

    if ((bytes = ftell (file)) == -1) {     /* get number of bytes */

        fprintf (stderr, "error: unable to determine file length.n");

        return NULL;

    }

    fseek (file, 0, SEEK_SET);              /* fseek beginning of file */



    /* allocate memory for file */

    if (!(file_content = malloc (bytes))) { /* allocate/validate memory */

        perror ("malloc - virtual memory exhausted");

        return NULL;

    }



    /* read all data into file in single call to fread */

    if (fread (file_content, 1, (size_t)bytes, file) != (size_t)bytes) {

        fprintf (stderr, "error: failed to read %ld-bytes from '%s'.n",

                bytes, fname);

        return NULL;

    }

    fclose (file);              /* close file */

    *nbytes = (size_t)bytes;    /* update nbytes making size avialable */



    return file_content;        /* return pointer to caller */

}



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



    size_t nbytes;

    char *content;



    if (argc < 2) {     /* validate required argument givent */

        fprintf (stderr, "error: insufficient input. filename req'd.n");

        return 1;

    }



    if ((content = read_file (argv[1], &nbytes))) { /* read/validate */

        printf ("read %zu bytes of data from %sn"

                "------content------n%sn-------------------n", 

                nbytes, argv[1], content);

        free (content);

    }



    return 0;

}

Example Input File

$ cat dat/foo.txt

"Foo bar!!"

Example Use/Output

$ ./bin/freadbinfoo dat/foo.txt

read 12 bytes of data from dat/foo.txt

------content------

"Foo bar!!"



-------------------

Don't forget to use a memory use & error checking program (like valgrind on Linux) to insure there are no memory errors and that you have freed all memory you have allocated.

Here's a simple example of how to do this:

#include <stdio.h>

#include <stdlib.h>

#include <sys/stat.h>

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

    char *fname = "./someFileNameHere";

    struct stat st;

    stat(fname, &st);

    char *content = malloc(st.st_size+1);

    content[st.st_size] = 0;

    FILE *infile = fopen(fname, "rb");

    size_t read = fread(content, sizeof(char), st.st_size, infile);

    fclose(infile);

    puts(content);

    return 0;

}

I've left all of the necessary error handling to you.