Question

So I have a program that makes char* stuff lowercase. It does it by iterating through and manipulating the ascii. Now I know there’s probably some library for this in c++, but that’s not the point – I’m a student trying to get a grasp on char*s and stuff :).

Here’s my code:

#include <iostream>  using namespace std;  char* tolower(char* src);  int main (int argc, char * const argv[]) {     char* hello = 'Hello, World!\n';      cout << tolower(hello);     return 0; }  char* tolower(char* src) {     int ascii;     for (int n = 0; n <= strlen(src); n++)     {         ascii = int(src[n]);         if (ascii >= 65 && ascii <= 90)         {             src[n] = char(ascii+32);         }     }      return src; } 

( this is not for an assignment 😉 )

It builds fine, but when I run it it I get a ‘The Debugger has exited due to signal 10’ and Xcode points me to the line: ‘src[n] = char(ascii+32);’

Thanks!

Mark

Answer 1

Yowsers!

Your ‘Hello World!’ string is what is called a string literal, this means its memory is part of the program and cannot be written to.

You are performing what is called an ‘in-place’ transform, e.g. instead of writing out the lowercase version to a new buffer you are writing to the original destination. Because the destination is a literal and cannot be written to you are getting a crash.

Try this;

char hello[32]; strcpy(hello, 'Hello, World!\n'); 

Also in your for loop, you should use <, not <=. strlen returns the length of a string minus its null terminator, and array indices are zero-based.