Sort in alphabetically order random names in C

Question

I try to sort alphabetically some names but get the "Segmentation Fault (core dumped)" error when I try to copy one string to another using bubble sort method. Here is my code:

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

int main() {
    char *string[] = {"Nickole", "Bolden", "Eldon", "Darcie", "Lisette", "Furr", "Parthenia", "Tunison", "Andrew", "Michael"};
    char *hold;
    int compare_a, compare_b;
    for(int j = 0; j < 9; j++) {
        for(int i = 0; i < 9; i++) {
            compare_a = string[i][0];
            compare_b = string[i+1][0];
            if( compare_a > compare_b) {           
                strcpy(hold, string[i+1]);
                strcpy(string[i+1], string[i]);
                strcpy(string[i], hold);
            }
        }
    }
    for(int i = 0; i < 9; i++) {
        printf("%s ", string[i]);
    }
    return 0;
}

`string` is an array of string literals. You cannot write over this memory with `strcpy()`. — Code-Apprentice, Jan 28 '18 at 17:18
Instead of copying the strings, you should just swap the pointers to each string. — Code-Apprentice, Jan 28 '18 at 17:19
You cannot modify a string literal. Also, there are countless of examples of how to sort an array of pointers to char alphabetically if you google for them. — Antti Haapala -- Слава Україні, Jan 28 '18 at 17:29
Possible duplicate of [Why do I get a segmentation fault when writing to a string initialized with "char \*s" but not "char s\[\]"?](https://stackoverflow.com/questions/164194/why-do-i-get-a-segmentation-fault-when-writing-to-a-string-initialized-with-cha) — n. m. could be an AI, Jan 28 '18 at 17:46

score 1 · Answer 1 · answered Jan 28 '18 at 17:24

The memory of holdis never allocated. With strcpy(hold, ..) that will be an issue. Better to use char hold[MAX_NAME_LENGTH]; or allocate with new corrsponding Memory resources.

Additional the array string is a compile time constant Array which you can't override.

J...S · Accepted Answer · 2018-01-28T18:04:08.957

The strings you have in your program are string literals. Literals are like constants and attempts to modify them leads to undefined behaviour though they are not specified as const. They may be placed in a part of memory from which the program will only be able to read but not write.

You attempt to modify the memory where the string literals are stored with your strcpy()s. You got a segmentation fault because you invoked undefined behaviour.

Now your program would've worked had you declared the strings like

char string[][10] = {"Nickole", "Bolden", "Eldon", "Darcie", "Lisette", "Furr", "Parthenia", "Tunison", "Andrew", "Michael"};

I gave the size as 10 as the longest string here is of length 9. One byte extra for the \0 character indicating end of string.

This is because they are not string literals and may be modified.

See this post.

As Code-Apprentice suggested in the comments you could swap the values of pointers instead of attempting to swap string literals.

if( compare_a > compare_b) {
    hold=string[i];
    string[i]=string[i+1];
    string[i+1]=hold;
}

Also, you can use strcmp() for comparing strings instead of just comparing the first character of the strings like

if( strcmp(string[i], string[i+1])>0 ) {
    hold=string[i];
    string[i]=string[i+1];
    string[i+1]=hold;
}

strcmp() returns positive value if the second string is before the first in the lexicographical order.

I got "error: assignment to expression with array type" at the line with 'hold=string[i]' — Co_Co, Jan 28 '18 at 17:57

Sort in alphabetically order random names in C

2 Answers2