Array of pointers with malloc

Question

I have to do a task for university c course and I'm stuck (i won't ask you to write it for me, it's just a simple question). I need to:

malloc an array of pointers in which i'll save adresses of memory assinged to strings, which i'll enter
activate function n times (n-number of strings) in which i enter the string and save it to its assigned memory
activate function which sorts (with bubblesort) the array of pointers in alphabetical order of entered strings.
print sorted strings.

i'm stuck here:

void enter(char *pointer[], int b, int l)
{
    char temp[l];
    printf("Enter string: ");
    scanf("%s",temp);
    printf("Test: %s; %d \n",temp, &temp);
    pointer[b]=temp;
    printf("Test: %s; %d \n",pointer[b], &pointer[b]);
}

void druga()
{
    int i, ile=1, leng=100;
    char *wsk[ile];
    for(i=0;i<ile;i++) wsk[i]=(char*)malloc(leng*sizeof(char));
    
 
    for(i=0;i<ile;i++) 
    {
        enter(wsk,  i, leng);
    }
    for(i=0;i<ile;i++) 
    {
        printf("Test2 %s; %d \n", wsk[i], &wsk[i]);
            
    }
    //bubblesort(wsk);
   
}

int main(void)
{
    druga();
    return 0;
}

Output:

Enter string: asd
Test: asd; -402654896 
Test: asd; -402654688
Test2 ; -402654688

The issue is that somehow the string does not pass to druga() function. Does anyone have a solution? Thanks for help

pointer[b]=temp; copies the pointer, not the contents of temp and temp is invalid once the function ends. Research strdup() and strcpy(). — chux
– chux, Commented Jan 4, 2022 at 19:46
I attempted running your code myself without changing anything, and my last line of output was Test2 asd; 1784384112, seems that the string is being passed fine, maybe try running it in a different environment? — Ewan Brown
– Ewan Brown, Commented Jan 4, 2022 at 19:48
Your homework glosses over step 0, in which you allocate the space for the strings themselves. — Neil
– Neil, Commented Jan 4, 2022 at 20:11

0___________ · Accepted Answer · 2022-01-04 20:27:05Z

1

    char temp[l];

is a local automatic storage variable and it cannot be accessed via the pointer after the function exit, as this variable stops existing.

You have many less important issues in your code as well.

void enter(char *pointer[], int b, int l)
{
    char temp[l];
    printf("Enter string: ");
    scanf("%s",temp);
    printf("Test: %s; %p \n",temp, (void *)temp);
    strcpy(pointer[b], temp);
    printf("Test: %s; %p \n",pointer[b], (void *)pointer[b]);
}

void druga()
{
    int i, ile=1, leng=100;
    char *wsk[ile];
    for(i=0;i<ile;i++) wsk[i]=malloc(leng*sizeof(**wsk));
    
 
    for(i=0;i<ile;i++) 
    {
        enter(wsk,  i, leng);
    }
    for(i=0;i<ile;i++) 
    {
        printf("Test2 %s; %p \n", wsk[i], (void *)wsk[i]);
            
    }
    //bubblesort(wsk);
   
}

int main(void)
{
    druga();
    return 0;
}

This program should also free dynamically allocated memory, check for the allocation errors, check the result of scanf and limit number of entered characters to do not write outside the temp array bounds.

edited Jan 4, 2022 at 20:27

answered Jan 4, 2022 at 20:09

0___________

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2 Comments

0___________ Over a year ago

@chux-ReinstateMonica did not not noticed it in

Caligula Over a year ago

Your answers were helpful, thank you both. Code works perfectly

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