Segmentation Fault in algorithm to separate strings

Question

I'm learning C by myself and I'm trying to use my knowledge (i.e. no library use) to create a program that does the following:

Split a string into words (words are separated by spaces)
Put each word in an array

So, in the end, I must have an array of strings (an array of array of chars).

This is my code:

#include <stdio.h>

int main () {
int i, conta, indice_completo=0, indice_nome=0, indice_caractere=0;
char nome [90], nomevetor [30] [90];


scanf ("%[^\n]s", nome);

while (nome[indice_completo] != '\0') {
    while (nome[indice_completo] != ' ' && nome [indice_completo] != '\0') {
        nomevetor [indice_nome] [indice_caractere] = nome [indice_completo];
        indice_completo++;
        indice_caractere++;
    }
    nomevetor [indice_nome] [indice_caractere] = '\0';
    indice_caractere=0;
    indice_nome++;
}
conta=indice_nome;

for (i=0 ; i<conta; i++) {
    printf ("Nome %d: %s\n", i+1, nomevetor [i]);
}

return 0;
}

But when I compile it using:

gcc -ansi -Wall -g programa.c -o programa

I get segmentation fault.

Why did I get segmentation fault?
Is my algorithm correct?
Is there a better way to do what I want?

I've corrected your English a bit.

Maria Ines Parnisari
– Maria Ines Parnisari

2013-11-17 20:26:28 +00:00
Commented Nov 17, 2013 at 20:26 — Maria Ines Parnisari
– Maria Ines Parnisari, Commented Nov 17, 2013 at 20:26

Jonathan Leffler · Accepted Answer · 2013-11-17 20:32:33Z

Your coding problem is that when you reach a blank in the input, you don't ever get past it.

Add a loop:

while (nome[indice_completo] == ' ')
    indice_completo++;

just before the end of the main loop.

Fixed code:

#include <stdio.h>

int main(void)
{
    int i, conta, indice_completo = 0, indice_nome = 0, indice_caractere = 0;
    char nome[90], nomevetor[30][90];


    scanf("%[^\n]s", nome);

    while (nome[indice_completo] != '\0')
    {
        while (nome[indice_completo] != ' ' && nome[indice_completo] != '\0')
        {
            nomevetor[indice_nome][indice_caractere] = nome[indice_completo];
            indice_completo++;
            indice_caractere++;
        }
        nomevetor[indice_nome][indice_caractere] = '\0';
        printf("Word: <<%s>>\n", nomevetor[indice_nome]);
        indice_caractere = 0;
        indice_nome++;
        while (nome[indice_completo] == ' ')
            indice_completo++;
    }
    conta = indice_nome;

    for (i = 0; i < conta; i++)
    {
        printf("Nome %d: %s\n", i+1, nomevetor[i]);
    }

    return 0;
}

Example run:

$ ./segfault
Arterial blockage I believe
Word: <<Arterial>>
Word: <<blockage>>
Word: <<I>>
Word: <<believe>>
Nome 1: Arterial
Nome 2: blockage
Nome 3: I
Nome 4: believe
$

(Only the program is now misnamed — it doesn't seg fault any more.)

You need to make sure nothing overflows the limits, too. Mainly, that would be using %89[^\n] in the format string, since you can't have more than 45 alternating non-blank and blank in a 90-character buffer.

If the input starts with a blank, the first 'word' will be empty. You could fix that by putting the 'skip' loop at the top of the main loop.

Roddy · Accepted Answer · 2013-11-17 20:31:59Z

1

Looks good overall, but when you detect a space, you still need to increment indice_completo otherwise you'll never get past it.

And then, you'l keep on incrementing indice_nome until you fall off the end of the array, hence the seg fault.

answered Nov 17, 2013 at 20:31

Roddy

68.5k46 gold badges173 silver badges282 bronze badges

Collectives™ on Stack Overflow

Segmentation Fault in algorithm to separate strings

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related