Keeping the value of a String initialized into a function - c

Question

I know my title isn't clear, It will be clearer with code + examples.
I want to initialize a char* ("motSecret" in the main, "mot" in my function) containing a word selected randomly into a file, doing this into a function. This array is made dynamic using memory allocation.
The variable in my function get well initialized, but when I print the value just after I exited the function, the value change and become something like "0#"
Here is the part concerned in the main :
int main()
{
FILE* dico =NULL;
char *motSecret, *motRes;
char lettre=' ';
int check=0, nbCoups=10, longueur=0, nbMots=0;
Bool erreur = TRUE;
srand(time(NULL));
nbMots = scanDico(dico);
getWord(dico, nbMots, motSecret);
printf("Mot : %s", motSecret);
The problem appears after the function getWord(). Here is the code of this function :
void getWord(FILE* dico, int nbLignes, char *mot)
{
int numMotChoisi=rand() % nbLignes, nbChar=0;
char charActuel=' ';
dico = fopen("dico.txt", "r");
rewind(dico);
if(dico != NULL)
{
while (numMotChoisi > 0)
{
charActuel = fgetc(dico);
if (charActuel == '\n')
numMotChoisi--;
}
charActuel = ' ';
while(charActuel != '\n')
{
charActuel = fgetc(dico);
nbChar++;
}
fseek(dico,-(nbChar)-1,SEEK_CUR);
mot = malloc(nbChar * sizeof(char));
if(mot == NULL)
{
printf("Probleme d'allocation memoire");
exit(0);
}
fgets(mot, SIZE, dico);
mot[strlen(mot) - 1] = '\0';
printf("Mot = %s ", mot);
}
fclose(dico);
}
The printf at the end of the function return a good value, and the printf just after the getWord() in the main show that the value changed in the function haven't been "saved"...
Other thing, that works fine without memory allocation.
I hope I'm clear enough. If I forgot to tell something or if you need more informations, please tell me.

Answer 1

C uses pass by value in function parameter passing.
You need a double pointer, something like void getWord(FILE* dico, int nbLignes, char **mot) if you want to allocate memory inside another function.
As a cascased effect, printf("Mot : %s", motSecret); is trying to access uninitialized memory, causing undefined behaviour.
Suggestions:
I see no reason to use FILE *dico as a parameter in getWord(). In can very well be a local.
instead of using double pointer, i would like to recommend returning the allocated pointer from getWord(), i.e., change void getWord() to char * getWord(), add return mot and use like motSecret = getWord(<params>)

Answer 2

char *motSecret;
motSecret is a local variable withing main() and it is not initilized.
By calling
getWord(dico, nbMots, motSecret);
You are passing some uninitialized pointer to a function getword().
Inside getword() you are assigning some memory to
char *mot;
and writing some data to this memory.
Now this memory is not known to motSecret You have to return this memory address to the uninitialized pointer in main()
char *motSecret = getWord(dico, nbMots);
Your getword() should be like,
char *getWord(dico, nbMots);
and inside this after performing everything do,
return mot;