Lowercase to uppercase letters problems in C - segmentation fault

Question

i have a segmentation fault error when i want to run the executable file

void lowerupper(char *s){
    int i ;

    int a = strlen (s);

    printf("%d\n", a);

    //fails here segmentation fault

    for (i=0 ; i < a-1 ; i++){

        if( (s[i] >= 97) && (s[i] <= 122)){
             s[i] = s[i] - 32;
        }
    }
}

int main(void) {

   char* string1 = 'HeLlo wOrlD';

   printf("%s\n", string1);

   lowerupper(string1);

   printf("%s\n", string1);

   return 0;
}

Maybe but the loop `for (i=0 ; i < a-1 ; i++)` is wrong because it ignores the last character in the string. `strlen` does not include the `nul` terminator. It should be `i < a` — Weather Vane, Oct 01 '17 at 17:43

score 1 · Answer 1 · edited Oct 01 '17 at 18:00

1

You can not modify string1. In fact when you declare a string like this

 char* string1 = "HeLlo wOrlD";

The string could be stored into a READ-ONLY memory area, it means that you can read it, but not modify it. If you do

char array[] = "hello world";

Then it creates a read-only string, and copies the characters into array, you'll be able to modify it (into array). You are invited to declare read-only strings with the keyword const.

 const char *string1 = "HeLlo wOrlD";

edited Oct 01 '17 at 18:00

Weather Vane

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answered Oct 01 '17 at 17:03

Gam

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A pointer is not a string, nor is an array per-se. C does not have a string type. – too honest for this site Oct 01 '17 at 17:33
@Olaf Yes, I was a bit clumsy, it's not always easy to find the right words to talk about that :( – Gam Oct 01 '17 at 17:47

score -1 · Answer 2 · edited Oct 01 '17 at 18:02

-1

You might have been passing address of local variable to the function. You should allocate memory in heap and then pass that variable to function. This code works here:

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

void lowerupper(char *s)
{
    int i ;
    int a = strlen (s);
    printf("%d\n", a);

    for (i=0 ; i < a-1 ; i++)
    {
        if( (s[i] >= 97) && (s[i] <= 122))
        {
             s[i] = s[i] - 32;
        }
    }
}

int main(void) 
{
    char *ss=malloc(10);
    strcpy(ss,"hello\n");
    lowerupper(ss);
    printf("%s",ss);
    return 0;
}

Sample Output:

6

HELLO

edited Oct 01 '17 at 18:02

0___________

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answered Oct 01 '17 at 16:59

krpra

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Not necessary . – too honest for this site Oct 01 '17 at 17:33
@Olaf yeah but might be possible – krpra Oct 01 '17 at 17:37
@PeterJ_01 Thanks Sir, I never say that my answer is right, But through this I learned something new from you people, next time I'll try more better. – krpra Oct 01 '17 at 18:07
1

if you give **the answer** you must be 100% percent sure, This is not a point or reputation race. – 0___________ Oct 01 '17 at 18:09
@PeterJ_01 yeah I agree with you but 1st thing is to try and I am trying, I'll be 100% sure from next time as I learnt today. – krpra Oct 01 '17 at 18:14

Lowercase to uppercase letters problems in C - segmentation fault

2 Answers2