std::sort on a c-style string, without copying the string

Question

I've run into a strange, and very specific issue. As some background, I need to support some legacy code that's passing around a lot of large c-style strings. Since these get pretty gigantic, I want to avoid unnecessarily copying that data, which would include copy constructing std::strings just for one operation.

I want to use std::sort on these strings, but they obviously lack iterators. However, according to the documentation for std::sort, I should just be able to pass in two pointers for any contiguous random access memory, but it isn't working with my c-style string

Basically it's like this:

char* foo = "test string";
std::sort(foo, foo + 11);    // access violation occurs

However:

char foo[] = "test string";
std::sort(foo, foo + 11);    // perfect fine, sorted correctly

This is extra confusing to me, because as far as I know, char* and char[] are essentially the same. Why does char* break, while char[] succeeds? How can I pass a c-style string into an STL algorithm?

`char* foo = "test string";` should give you a compilation warning/error. — Richard Critten, Apr 14 '17 at 18:52
"but they obviously lack iterators" ... pointers are obviously iterators — 463035818_is_not_an_ai, Apr 14 '17 at 18:52
*"because as far as I know, char* and char[] are essentially the same."* Not really, no. — Baum mit Augen, Apr 14 '17 at 18:54
Also, that was not hard to google. Please do some research before asking. — Baum mit Augen, Apr 14 '17 at 18:55
If you are sorting the characters in a string, as opposed to a vector of strings, you should consider a counting sort, which could be a lot faster on long strings. — rici, Apr 14 '17 at 19:05

score 4 · Accepted Answer · edited May 23 '17 at 11:54

char* foo = "test string";

This is a pointer to a string literal, which is stored in read-only memory, thus you cannot modify/sort it.

Your code should be giving you a warning, similar to this:

Georgioss-MacBook-Pro:~ gsamaras$ g++ -Wall main.cpp 
main.cpp:3:17: warning: conversion from string literal to 'char *' is deprecated
      [-Wc++11-compat-deprecated-writable-strings]
    char* foo = "test string";
                ^

Please read: What is the difference between char s[] and char *s?

std::sort on a c-style string, without copying the string

1 Answers1