C program, printf char* crashes

Question

I have a structure which is composed of a char* and many attributes.

I can't print my char* as a string, it just crashes.

Here is my code :

int main() {
    sommet_t* sommet = creerSommet("rouge", 5, NULL);
    printf("Couleur : %s", sommet->couleur);
    return 0;
}

And my sommet.c :

sommet_t* creerSommet(char* couleur, int distance, sommet_t* pere) {
    sommet_t* sommet =  malloc(sizeof(sommet_t));
    sommet->distance = distance;
    sommet->couleur = (char*)malloc((strlen(couleur)+1) * sizeof(char));
    strcpy(sommet->couleur,couleur);
    sommet->pere = pere;
}

I absolutely don't know what's wrong in it.

Edit : sommet.h

#ifndef __SOMMET_H__
#define __SOMMET_H__

typedef struct sommet_type {
    char *couleur;
    int distance;
    struct sommet_type *pere;
} sommet_t;

sommet_t* creerSommet(char*, int, sommet_t*);

#endif

`sizeof(char)` in `(char*)malloc((strlen(couleur)+1) * sizeof(char));` is redundant and unnecessary. — Fiddling Bits, Jan 07 '17 at 15:59
[Please see this discussion on why not to cast the return value of `malloc()` and family in `C`.](http://stackoverflow.com/q/605845/2173917). — Sourav Ghosh, Jan 07 '17 at 16:00
___Please don't change code in question in a way which makes the answers invalid.___ — Sourav Ghosh, Jan 07 '17 at 16:05

score 3 · Answer 1 · answered Jan 07 '17 at 15:53

3

You should return the object from the function creerSommet

sommet_t* creerSommet(char* couleur, int distance, sommet_t* pere) {
    sommet_t* sommet =  malloc(sizeof(sommet_t));
    sommet->distance = distance;
    sommet->couleur = (char*)malloc((strlen(couleur)+1) * sizeof(char));
    strcpy(sommet->couleur,couleur);
    sommet->pere = pere;
    return sommet;
}

answered Jan 07 '17 at 15:53

cokceken

2,068
11
22

Thanks, I added it but it still crashes – Xnate Maxime Jan 07 '17 at 15:59
sommet->couleur = (char*)malloc((strlen(couleur)+1) * sizeof(char)); Isn't this only ever allocating space for one character since coleur is uninitialized at this stage, or worse, maybe some length of garbage data? – synchronizer Jan 07 '17 at 15:59
@synchronizer couleur is my parameter which is "rouge" – Xnate Maxime Jan 07 '17 at 16:03
@synchronizer that's the function parameter. – Sourav Ghosh Jan 07 '17 at 16:03
If I try to display "distance", it displays 0 instead of 5 but it is not crashing. :( – Xnate Maxime Jan 07 '17 at 16:19

score 1 · Answer 2 · edited May 23 '17 at 12:24

1

You forgot to return sommet from the function.

FWIW, any function, which is expected to return some value, if does not return a value, and the return value is used in caller, it invokes undefined behavior.

Quoting C11, chapter §6.9.1, Function definitions

If the } that terminates a function is reached, and the value of the function call is used by the caller, the behavior is undefined.

That said,

Please see this discussion on why not to cast the return value of malloc() and family in C.
Always check for success of malloc() before using the returned pointer.
sizeof(char) is guaranteed to be 1 in C. Using it as a multiplier is redundant.

edited May 23 '17 at 12:24

Community

1
1

answered Jan 07 '17 at 15:53

Sourav Ghosh

133,132
16
183
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Oh that's it, I got no error in IDE or compiler, got to pay more attention with this language :( – Xnate Maxime Jan 07 '17 at 15:54
It still crashing tho :x – Xnate Maxime Jan 07 '17 at 15:56
2

enable warnings... or use a proper compiler. This problem is trivial to catch. – Karoly Horvath Jan 07 '17 at 15:58
Using codeblocks with GNU GCC Compiler, can you give me any good one please ? – Xnate Maxime Jan 07 '17 at 16:01
@XnateMaxime: enable warnings. – Karoly Horvath Jan 09 '17 at 13:59

C program, printf char* crashes

2 Answers2