How can I return file contents from a function?

Question

I am writing a C library. I want to return the contents of a file from this function to the caller.

How can I convert the file contents to char[]?

fopen is crashing since I am using perl.h in my C code. Is there any other way to convert file into a char array apart from opening & reading the file?

Here is my code:

FILE* fp = fopen("console.txt", "r");
char message[1024];
strcpy(message,"\n");

char buf[80];
while(!feof(fp))
{
    fgets(buf, sizeof(buf)-1, fp);
    strcat(message, buf);
}

This might (partially) help: http://stackoverflow.com/questions/2029103/correct-way-to-read-a-text-file-into-a-buffer-in-c — Patrick B., Nov 25 '11 at 17:19

score 2 · Accepted Answer · edited May 23 '17 at 12:03

2

Get the file size (see How can I get a file's size in C?)
Allocate memory to store contents of the file (see malloc).
Read contents of the file into allocated memory (see read).
Return a pointer and a length of data in bytes to the user.

Don't forget to check for errors in between those steps.

edited May 23 '17 at 12:03

Community

1
1

answered Nov 25 '11 at 17:22

score 1 · Answer 2 · answered Aug 31 '17 at 05:04

Try this code. The function returns the string with file content, just print it.

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

    char *readFile(char *filename)
    {
        char * buffer = 0;
        long length;
        FILE * f = fopen (filename, "r");
        if (f)
        {
            fseek (f, 0, SEEK_END);
            length = ftell (f);
            fseek (f, 0, SEEK_SET);
            buffer = malloc (length);
            if (buffer)
            {
                fread (buffer, 1, length, f);
            }
            fclose (f);
        }
        return buffer;
    }

    int main()
    {
       char *content=readFile("D://test1.xml");
       printf("%s",content);
       return 0;
    }

score 1 · Answer 3 · answered Nov 25 '11 at 17:20

1

You need to do a few things

Determine size of file (checkout fstat/stat)
You need to malloc enough memory to hold the file
You can then use fread to read the conents of the file into your array (dont forget to open the file in binary mode)
Return you pointer (and dont forget that it has to be freed after by the function caller)

answered Nov 25 '11 at 17:20

Adrian Cornish

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Need to return the length if null characters are in it - otherwise `strlen` will not work! – Ed Heal Nov 25 '11 at 17:22

score 0 · Answer 4 · answered Nov 25 '11 at 17:21

Bit more information is required to give a good answer as the contents and nature of the file is required.

But generally,

If it is a text file see the stdio library - you can get the length, create an array and fill it. Otherwise (binary files) parsing it would be a good idea and return a data structure - a lot more useful

How can I return file contents from a function?

4 Answers4