C++, best way to change a string at a particular index

Question

I want to change a C++ string at a particular index like this:

string s = "abc"; s[1] = 'a'; 

Is the following code valid? Is this an acceptable way to do this?

I didn't find any reference which says it is valid:

http://www.cplusplus.com/reference/string/string/

Which says that through "overloaded [] operator in string" we can perform the write operation.

Answer 1

Assigning a character to an std::string at an index will produce the correct result, for example:

#include <iostream> int main() {     std::string s = "abc";     s[1] = 'a';     std::cout << s; } 

For those of you below doubting my IDE/library setup, see jdoodle demo: http://jdoodle.com/ia/ljR, and screenshot: https://imgur.com/f21rA5R

Which prints aac. The drawback is you risk accidentally writing to un-assigned memory if string s is blankstring or you write too far. C++ will gladly write off the end of the string, and that causes undefined behavior.

A safer way to do this would be to use string::replace: http://cplusplus.com/reference/string/string/replace

For example

#include <iostream>  int main() {      std::string s = "What kind of king do you think you'll be?";      std::string s2 = "A good king?";      //       pos len str_repl      s.replace(40, 1, s2);      std::cout << s;        //prints: What kind of king do you think you'll beA good king? } 

The replace function takes the string s, and at position 40, replaced one character, a questionmark, with the string s2. If the string is blank or you assign something out of bounds, then there's no undefined behavior.