Assign value to char in array

Question

I'm trying to brush up on my C/C++ and I seem to have forgotten how to properly manipulate char arrays.

Code:

#include <iostream>
#include <string.h>

void reverse(char* str)
{
    int numChar = strlen(str);
    char *reversed = (char*)malloc(sizeof(char) * (numChar + 1));

    int i = numChar;
    int j = 0;
    while(i >= 0)
    {
        reversed[j] = str[i];
        j++;
        i--;
        printf("%c", reversed[j]);
    }

    printf("%s", reversed);
}

int main()
{
    char* str;
    strcpy(str, "apple\0");
    reverse(str);
    return 0;   
}

I'm very certain I'm not doing what I intend to with reversed[j] = str[i] as reversed comes out empty. What's the correct way to go about this?

Santosh A · Accepted Answer · 2014-08-12 04:48:56Z

From first glance, In main(), memory has to be allocated to character pointer str before referencing it in strcpy

int main()
{
    char* str = malloc(6)  or use char str[6];
    // or char *str = "apple"; is sufficient, strcpy is not required in this case 
    strcpy(str, "apple\0");
    reverse(str);
    return 0;   
}

Another one : In reverse() function, you will have to increment j after printing

while(i >= 0)
{
    reversed[j] = str[i];
    printf("%c", reversed[j]);
    j++;         //Moved here
    i--;
}
reversed[j] = '\0'          //Null termination

printf("\n %s", reversed);

or only the below two statements would be sufficient enough to post increment j and decrement i

reversed[j] = str[i--];
printf("%c", reversed[j++]);

Valdar Moridin · Accepted Answer · 2014-08-12 04:38:56Z

3

Since you start with i being the strlen of the input string (e.g. HAHA -> 4), you start copying at haha[4], which is the null byte at the end of the string. IOW you just null terminated your output right at the start. Try setting i to numChar - 1.

(After fixing the problem Santosh A mentioned)

And then, make sure you null terminate the result!

edited Aug 12, 2014 at 4:38

answered Aug 12, 2014 at 4:33

Valdar Moridin

2561 silver badge5 bronze badges

Collectives™ on Stack Overflow

Assign value to char in array

2 Answers 2

Comments

Comments

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Related