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

If you are only concerned with 8 bit characters (which all other answers except Milan Babuškov assume as well) you can get the fastest speed by generating a look-up table at compile time using metaprogramming. On ideone.com this runs 7x faster than the library function and 3x faster than a hand written version (http://ideone.com/sb1Rup). It is also customizeable through traits with no slow down.

template
struct IntVector{
using Type = IntVector;
};

template
struct PushFront;
template
struct PushFront,I_New> : IntVector{};

template>
struct Iota : Iota< I_Size-1, typename PushFront::Type> {};
template
struct Iota<0,T_Vector> : T_Vector{};

template
struct ToUpperTraits {
    enum { value = (C_In >= 'a' && C_In <='z') ? C_In - ('a'-'A'):C_In };
};

template
struct TableToUpper;
template
struct TableToUpper>{
    static char at(const char in){
        static const char table[] = {ToUpperTraits::value...};
        return table[in];
    }
};

int tableToUpper(const char c){
    using Table = TableToUpper::Type>;
    return Table::at(c);
}

with use case:

std::transform(in.begin(),in.end(),out.begin(),tableToUpper);

For an in depth (many page) decription of how it works allow me to shamelessly plug my blog: http://metaporky.blogspot.de/2014/07/part-4-generating-look-up-tables-at.html