char array input with space

Question

my program works fine if i give hard code value to char *w="ls -l" but i am trying to take input form user not working help my code:: using input error occur i don't understand the concept of fgets using fgets its gives the garbig value to execv

#include<stdio.h>
#include<sys/wait.h>
#include<stdbool.h>

void func(char **arr, char *w)
{
    int i = 0, j = 0, k = 0;

    char temp[100];

    for (i = 0; i < 100; i++)
    {
        if (w[i] == '')
        {
            arr[k] = temp;
            arr[k+1] = NULL;
            break;
        }
        if (w[i] == ' ')
        {
            arr[k] = temp;
            k++;
            j = 0;
        }
        else
        {
            temp[j] = w[i];
            j++;
        }

    }
}
int main()
{
    char *n = "/bin/ls";
    char *arr[10] = {''};
    char p[100] = {''};
    char *w = "ls -l";
    int i = 0;
    //printf("bilal-hassan-qadri $ >>");
    //fgets(p, 100, stdin);
    arr[2] = NULL;
    bool found = false;
    for (i = 0; i < sizeof(w); i++)
    {
        if (w[i] == ' ')
        {
            found=true;
            func(arr,w);
            break;
        }
    }
    if (!found)
      arr[0] = w;
    int status;
    int id = fork();
    if (id == 0)
    {
        if (execv(n,arr) < 0)
        {
            printf("invalid commandn");
        }
        else
        {
            printf("ninvalid command");
        }
    }
    else
    {
        wait(&status);
    }
}

If `fgets` is giving you trouble, you probably need to [remove the newline](http://stackoverflow.com/a/28462221/3386109) — user3386109, Oct 31 '15 at 21:40
`if (execv(n,arr) < 0) printf("invalid commandn"); else printf("ninvalid command");` - this is a bit weird to be honest. — user4520, Oct 31 '15 at 21:49
What do you want to do with `w[i] == ''`? It won't compile with gcc saying `error: empty character constant` — MikeCAT, Nov 01 '15 at 00:46

score 0 · Accepted Answer · answered Nov 01 '15 at 00:59

In the function func, You have to copy the string to elements of arr instead of just passing the address of temp, which will vanish on leaving the function. You can use strdup instead of copy_string if your system supports it.
You have to terminate the string in temp before copying it.
Empty string constant '' seems invalid. You shouldn't use it.
fgets stores new-line character \n if it exists. Check for it and remove if it isn't wanted.

Fixed code:

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<sys/wait.h>
#include<stdbool.h>

char *copy_string(const char *str) {
    char *s = malloc(strlen(str) + 1);
    if (s) strcpy(s, str); else {perror("malloc"); exit(1);}
    return s;
}

void func(char **arr, char *w)
{
    int i = 0, j = 0, k = 0;

    char temp[100];

    for (i = 0; i < 100; i++)
    {
        if (w[i] == '\0' || w[i] == '\n')
        {
            temp[j] = '\0';
            arr[k] = copy_string(temp);
            arr[k+1] = NULL;
            break;
        }
        if (w[i] == ' ')
        {
            temp[j] = '\0';
            arr[k] = copy_string(temp);
            k++;
            j = 0;
        }
        else
        {
            temp[j] = w[i];
            j++;
        }

    }
}
int main(void)
{
    char *n = "/bin/ls";
    char *arr[10] = {NULL};
    char p[100] = {0};
    char *w = "ls -l";
    int i = 0;
    //printf("bilal-hassan-qadri $ >>");
    fgets(p, 100, stdin);
    w = p;
    arr[2] = NULL;
    bool found = false;
    for (i = 0; w[i] != '\0'; i++)
    {
        if (w[i] == ' ')
        {
            found=true;
            func(arr,w);
            break;
        }
    }
    if (!found)
      arr[0] = w;
    int status;
    int id = fork();
    if (id == 0)
    {
        if (execv(n,arr) < 0)
        {
            printf("invalid commandn");
        }
        else
        {
            printf("ninvalid command");
        }
    }
    else
    {
        wait(&status);
        for (i = 0; arr[i] != NULL; i++) free(arr[i]);
    }
    return 0;
}

char array input with space

1 Answers1