CODEWITHSUNDEEP
cexecvp
Phil
Phil

Reputation: 327

Execvp not executing args

I can't get execvp to execute the args, this code only works if I set the number of args to 0. I've been trying to change lines here and there for 2 hours and checking other similar questions but nothing is working, maybe someone got an idea? 

void executeProgram()
{
    char *argv[20];
    printf("Please enter command or program name:");
    char *commande;
    scanf("%s", commande);
    argv[0] = malloc(100);
    argv[0] = commande;
    int nbArgZ = -1;
    while(nbArgZ < 0){
            printf("Please enter number of arguments:");
            scanf("%d", &nbArgZ);
    }
    int x;
    int y =1;
    for(x = 1; x < nbArgZ+1; x++){
            char *tempo;
            argv[x] = malloc(100);
            printf("Argument %d : ", x);
            scanf("%s", tempo);
            argv[x] = tempo;
            y++;
    }
    argv[y] = NULL;
    int pid = fork();
    if ( pid == 0 ) {
            execvp(argv[0], argv);
    }
    wait(2);
    printf( "End of execution\n");
}

Upvotes: 0

Views: 322

Answers (2)

pm100
pm100

Reputation: 50180

this code

   argv[0] = malloc(100);
    argv[0] = commande;

should set off alarm bells immediately. You assign something toe argv[0], then in the next line set it to something else. That cannot be correct

you need

char commande[100]; // we will assume 100 is enough
scanf("%s", commande);
argv[0] = strdup(commande); // strdup maybe not needed, buts lets be safe

and the same change inside your arg loop

Upvotes: 1

Some programmer dude
Some programmer dude

Reputation: 409176

You have multiple problems. Here are a couple of them:

argv[x] = malloc(100);
...
argv[x] = tempo;

First you make argv[x] point to some memory you allocate, then you make argv[x] point to where tempo is pointing, making you lose the original memory.

And about tempo:

char *tempo;
...
scanf("%s", tempo);

You have an uninitialized pointer. Where it is pointing is indeterminate and will seem almost random. Dereferencing this pointer, which happens when you call scanf, leads to undefined behavior.

Both of these issue can be solved by passing argv[x] directly to your scanf call:

scanf("%99s", argv[x]);  // No more than 99 characters (excluding terminator)

And you have the very same problem not once, but twice.

Upvotes: 2

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