No warning at implicit removal of const. Was: relearning C: why does an in-place change to a char* segfault?

On Thu, 01 Aug 2024 08:06:57 +0000
Mark Summerfield <mark@qtrac.eu> wrote:

This program segfaults at the commented line:
 
#include <ctype.h>
#include <stdio.h>
 
void uppercase_ascii(char *s) {
    while (*s) {
        *s = toupper(*s); // SEGFAULT
        s++;
    }
}
 
int main() {
    char* text = "this is a test";
    printf("before [%s]\n", text);
    uppercase_ascii(text);
    printf("after  [%s]\n", text);
}
 

The answers to your question are already given above, so I'd talk about
something else. Sorry about it.

To my surprise, none of the 3 major compilers that I tried issued the
warning at this line:
  char* text = "this is a test";
If implicit conversion of 'const char*' to 'char*' does not warrant
compiler warning than I don't know what does.
Is there something in the Standard that explicitly forbids diagnostic
for this sort of conversion?

BTW, all 3 compilers issue reasonable warnings when I write it slightly
differently:
  const char* ctext = "this is a test";
  char* text = ctext;

I am starting to suspect that compilers (and the Standard?) consider
string literals as being of type 'char*' rather than 'const char*'.