How to Convert a String to Upper Case in C++

c++string

How could one convert a string to upper case. The examples I have found from googling only have to deal with chars.

#include <algorithm>
#include <string>

std::string str = "Hello World";
std::transform(str.begin(), str.end(), str.begin(), ::toupper);

You need to put a double colon before toupper:

transform(input.begin(), input.end(), input.begin(), ::toupper);

Explanation:

There are two different toupper functions:

toupper in the global namespace (accessed with ::toupper), which comes from C.
toupper in the std namespace (accessed with std::toupper) which has multiple overloads and thus cannot be simply referenced with a name only. You have to explicitly cast it to a specific function signature in order to be referenced, but the code for getting a function pointer looks ugly: static_cast<int (*)(int)>(&std::toupper)

Since you're using namespace std, when writing toupper, 2. hides 1. and is thus chosen, according to name resolution rules.