Convert a String In C++ To Upper Case

Question

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

Answer 1

struct convert {
   void operator()(char& c) { c = toupper((unsigned char)c); }
};

// ... 
string uc_str;
for_each(uc_str.begin(), uc_str.end(), convert());

Note: A couple of problems with the top solution:

21.5 Null-terminated sequence utilities

The contents of these headers shall be the same as the Standard C Library headers , , , , and [...]

• Which means that the cctype members may well be macros not suitable for direct consumption in standard algorithms.

• Another problem with the same example is that it does not cast the argument or verify that this is non-negative; this is especially dangerous for systems where plain char is signed. (The reason being: if this is implemented as a macro it will probably use a lookup table and your argument indexes into that table. A negative index will give you UB.)