Copy value of char array to 2D array

Question

As you can see below i create a 2D array of strings. Also i use a char array named "buffer". I want to copy the value of buffer to the [5][0] position of the 2D array. The problem is that when the value of buffer changes, the value of the cell of the array also changes. I want to keep the first value.

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

char * strNameList[10][2] = { 
    {"Luca", "Daniel"} ,
    {"Vivan", "Desmond"},
    {"Abdul", "Justin"}, 
    {"Nina", "Marlene"},
    {"Donny", "Kathlene"} 
};

int main()
{
    int j, i;
    int pos = 5;
    char buffer[10204];

    strcpy(buffer, "A Value");

    strNameList[pos][0] = buffer;
    strNameList[pos][1] = "Surname";
    for (i = 0; i < 9; i++) {
        printf("\n");
        for (j = 0; j < 2; j++)
            printf(" %s", strNameList[i][j]);
    }

    strcpy(buffer, "B Value");      
    for (i = 0; i < 9; i++) {
        printf("\n");
        for (j = 0; j < 2; j++)
            printf(" %s", strNameList[i][j]);
    }
}

Output:

 Luca Daniel
 Vivan Desmond
 Abdul Justin
 Nina Marlene
 Donny Kathlene
 A Value Surname


 Luca Daniel
 Vivan Desmond
 Abdul Justin
 Nina Marlene
 Donny Kathlene
 B Value Surname

So what actually is your problem then? Be specific about it. — Manav Dubey
– Manav Dubey, Commented Mar 22, 2017 at 22:41

Iharob Al Asimi · Accepted Answer · 2017-03-22 22:44:41Z

1

The problem is that strNameList[pos][0] points to buffer and it's not an independant storage location, since it's simply a pointer you can modify it using either buffer or strNameList[pos][0] because both point to the same place in memory.

Don't mix pointers to string literals, and pointers to non-const arrays in the same array of strings, instead use

strNameList[pos][0] = strdup(buffer);

and you will see the difference, likewise

strNameList[pos][1] = strdup("Surname");

you will need a

free(strNameList[pos][0]);
free(strNameList[pos][1]);

later, when you no longer need the pointers.

answered Mar 22, 2017 at 22:44

Iharob Al Asimi

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