c++ - ::tolower vs std::tolower difference -

this question has answer here:

i have

using namespace std; vector<char> tmp; tmp.push_back(val); ...

now when try

transform(tmp.begin(), tmp.end(), tmp.begin(), std::tolower);

it fails compile, compiles:

transform(tmp.begin(), tmp.end(), tmp.begin(), ::tolower);

what's problem std::tolower? works 1 argument, e.g., std::tolower(56) compiles. thanks!

std::tolower has 2 overloads , cannot resolved unaryoperation c version ::tolower not.

if want use std::tolower can use lambda as

transform(tmp.begin(), tmp.end(), tmp.begin(), [](unsigned char c) {return std::tolower(c); });

Dil