C toLowerCase Function won't work - Access violation

Question

Hi,

I have a simple function which takes an array of characters as an argument, and converts all the characters to lower case. However, I get a weird access violation error. Here's the code:

void toLower(char *rec)
{
 int i=0;
 while (rec[i]!='\0')
 {
  if (rec[i]>='A' && rec[i]<='Z') 
               rec[i]='a'+rec[i]-'A';  //this is where I get an error - assigning the
                                       //the value to rec[i] is the problem
  i++;
 }
}

Can you tell me what's my mistake? Thanks

Answer 1

You're working too hard :)

#include <algorithm> //For std::transform
#include <cctype> //For std::tolower
#include <cstring> //For std::strlen

void toLower(char *rec)
{
    std::transform(rec, rec + std::strlen(rec), rec, std::tolower);
}

Answer 2

Sounds like you didn't pass in a valid buffer. But don't write this yourself; use something like strlwr.

Answer 3

Are you passing in (even indirectly) a string literal? If so, then it may be loaded in unwriteable memory; you'll need to make changes on a copy.

That your function prototype takes a char * rather than a const char * suggests that you've probably not done this, but I thought I`d throw it out.

Answer 4

In a comment you say that you pass in a literal string to the function, like this:

palindrome("In girum imus nocte et consumimur igni")

where palindrome passes its argument to toLower. This won't work because string literals are read-only and you are trying to modify it. Instead, you can use:

char str[] = "In girum imus nocte et consumimur igni";
palindrome(str);

Or you can have palindrome copy its argument into an array and call toLower on that.