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

Question

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

score 3 · Answer 1 · answered May 10 '13 at 06:35

3

Your code writes past the end of newstr and therefore has undefined behaviour.

Try either of the 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;

answered May 10 '13 at 06:35

NPE

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There's also potential undefined behavior by calling `::toupper` with a `char` as argument. – James Kanze May 10 '13 at 07:43

score 1 · Answer 2 · edited May 23 '17 at 12:03

1

You haven't got any space allocated for newstr.

See more here: C++ std::transform() and toupper() ..why does this fail?

edited May 23 '17 at 12:03

Community

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answered May 10 '13 at 06:36

Cristina_eGold

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but the newstr is "", isn't it? – jiafu May 10 '13 at 06:37
@jiafu Read the link deepdownunder2222 provides. `std::transform` has no way to enlarge `newstr`, so it runs out of space. – Gorpik May 10 '13 at 06:39

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

2 Answers2