c++ - why the result is nothing for this code sample about string toupper? -

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• c++ std::transform() , toupper() ..why fail? 3 answers

string str("fujian"); string newstr; transform(str.begin(), str.end(), newstr.begin(), ::toupper); cout << newstr << endl; 

why result nothing code sample string toupper?

your code writes past end of newstr , therefore has undefined behaviour.

try either of following instead:

// version 1 string str("fujian"); string newstr(str); transform(newstr.begin(), newstr.end(), newstr.begin(), ::toupper); cout << newstr << endl;  // version 2 string str("fujian"); string newstr; transform(str.begin(), str.end(), std::back_inserter(newstr), ::toupper); cout << newstr << endl;