将char **作为参数传递给C中的函数

Question

I know there are many topics of this kind but I've read several of them and still can't figure out what am I doing wrong.

I've successfully generated a char** array. My bubble sort function probably works as well. But when I passed the generated array to the function, only 1 row is copied.

#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<time.h>

void sort(char** tab)
{
        char* temp;
        int i, j, size = sizeof(tab)/sizeof(tab[0]);
        printf("%d\n", size);

        for(i = 0; i < size; ++i)
        {
                for(j = i+1; j < size; ++j)
                {
                        if(strcmp(tab[j-1], tab[j]) > 0)
                                strcpy(temp, tab[j-1]),
                                strcpy(tab[j-1], tab[j]),
                                strcpy(tab[j], temp);
                }
        }
        for(i = 0; i < sizeof(tab)/sizeof(tab[0]); ++i)
                puts(tab[i]);
}

int main()
{
        srand(time(NULL));
        int size = rand()%5+5, i, j, s;
        char** tab = (char**)malloc(size * sizeof(char*));

        for(i = 0; i < size; ++i)
        {
                s = rand()%9+1;
                tab[i] = (char*)malloc(s+1);
                for(j = 0; j < s; ++j)
                        tab[i][j] = 'a'+rand()%26;
                tab[i][s] = 0;
        }
        for(i = 0; i < size; ++i)
                puts(tab[i]);
        puts("");
        sort(tab);
        return 0;
}

Here 's how the code works.

And when I write size=5 before the loop in the function it returns segmentation fault.

Edit: Same with passing the size of the array as an argument: http://ideone.com/3Wvncq

Final code

I've fixed all the problems and here's the final code . I was misinterpreting segmentation fault as the result of assigning a fixed size instead of not allocating the temp variable. Thank you for all the answers.

Answer 1

Don't calculate size inside function void sort(char** tab) . As in this function it will be calculated as -

int i, j, size = sizeof(tab)/sizeof(tab[0]);   // equivalent to sizeof(char **)/sizeof(char*) in function giving wrong length as you desire.

It's length in main ( size is generated using rand so no need to find it) and then pass it as argument to function sort .

Declare your function like this -

void sort(char** tab,size_t size) 

And while calling from main pass length of tab to it -

sort(tab,size);  // size will be number of elements in tab calculated in main

You get segmentation fault because of this -

    if(strcmp(tab[j-1], tab[j]) > 0)
                 strcpy(temp, tab[j-1]),         
                 strcpy(tab[j-1], tab[j]),       
                 strcpy(tab[j], temp);

temp is uninitialized in sort and still you pass it to strcpy thus undefined behaviour . Initialize temp before passing to strcpy .Allocate memory to temp in function sort .

Answer 2

In your sort function you declare the temp variable:

char* temp;

Later you use it as destination (and source) for string copying:

strcpy(temp, tab[j-1]),

But nowhere in between do you make temp point anywhere, temp is uninitialized and that leads to undefined behavior and your crash.

Don't use a pointer, instead declare it as an array of the largest string size possible.