LinuxQuestions.org - [SOLVED] How to fill-up an pointer to an array of char in C

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How to fill-up an pointer to an array of char in C

I'm writing a little code, nothing fancy, which gets the open file from /proc/<pid>/maps:

Code:

#include <stdio.h>

#include <stdlib.h>

#include <string.h>



int main()

{

        FILE *file;

        char filename[1024];

        char input[4096];



        snprintf(filename, sizeof(filename), "/proc/1/maps");

        file = fopen(filename, "re");

        if (file) {

                while (fgets(input, 4096, file) != NULL) {

                        char *pos;



                        pos = strstr(input, "/");

                        if (pos != NULL) {

                                size_t len = strlen(pos);

                                if (pos[len - 1] == '\n')

                                        pos[len - 1] = '\0';

                        }

                }

        }



        return 0;

}

I would like to put all 'pos' into an char array or point char array, as you wish. I've tried some 'ideas', but all end-up with segfault or errors.

Never used a proper char array, so really not sure how to. Can anyone show me how or point me in the right direction?

when I've tried my luck, I've used something like:

Code:

char **s_array;

int count = 0;



s_array = calloc(1, sizeof(char *));

...

strcpy(s_array[count], pos);

count++;

s_array = realloc(s_array, (count + 1) * sizeof(char *);

...

but this didn't really work.

You need an array of pointers to arrays of characters (C strings). The outer array is of unknown length, so you can either read the file twice: once to determine the number of lines and then to read each line, or you can create an array that is "big enough"

Code:

char **s_array = calloc(4096, sizeof(char *)); // enough for 4096 strings

Then as you read in each string, allocate space for it and add it to the array.

Code:

size_t len = strlen(pos);

if (pos[len - 1] == '\n') {

    pos[len - 1] = '\0';

    len--;

}

if (count >= 4096)

    return EOVERFLOW;

s_array[count] = calloc(len + 1, sizeof(char));

strcpy(s_array[count], pos);

count++;

Sorry, but in calloc isn't the fist argument no_of_elements? Or am I reading wrong the documentation?

Never mind it simply takes the product of the two values
Also sizeof(char)==1. Plus there is a handy function called 'strdup'

Thanks guys, all worked.