Cant use the void func for converting string to Uppercase directly in if statement- c++

Question

I have void func below:

void ToUppercase(std::string & data)
{
    transform(data.begin(), data.end(), data.begin(), (int(*)(int))toupper);
}

if i use if statement like this:

if (ToUppercase(str).find("AAA") != string::npos) // Do something;

It is showing me error "expression must be a class type". Why cant i use void func directly in if statement. Somehow, it is not feasible for me to return value from ToUppercase func.

Ask yourself: What does `ToUppercase(str)` return? Can I call `find("AAA")` on that returned type? — NathanOliver, Sep 17 '18 at 14:58
You're trying to call the method `find` on a `void`. This doesn't make sense — Robert Kock, Sep 17 '18 at 15:00
Once again relevant: [Do I need to cast to unsigned char before calling toupper?](https://stackoverflow.com/q/21805674/3002139) — Baum mit Augen, Sep 17 '18 at 15:10

Armen Tsirunyan · Answer 1 · 2018-09-17T15:05:29.850

1

ToUppercase(str) is, as you've declared, of typevoid. You cannot call member access operator (.) on void.

If you want to chain calls like this you could also return the passed reference

std::string & ToUppercase(std::string & data)
{
    transform(data.begin(), data.end(), data.begin(), (int(*)(int))toupper);
    return data;
}

If you insist on returning void for some reason, your only valid option of doing what you're doing is:

ToUUppercase(str);
if(str.find("AAA") != std::string::npos)
{
}

edited Sep 17 '18 at 15:05

answered Sep 17 '18 at 14:59

Armen Tsirunyan

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**Improvement**: the generic `std::find` will probably be faster than `std::string::find` (see the comment section of https://www.bfilipek.com/2018/07/string-view-perf.html) – Matthias Sep 17 '18 at 15:11

score 1 · Answer 2 · edited Sep 17 '18 at 20:50

1

find() is a member method for the std::string class, but you are returning void instead. Reform your code to return a std::string so that you can call find() on the return value.

edited Sep 17 '18 at 20:50

Remy Lebeau

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answered Sep 17 '18 at 15:02

Muhammad Aly

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score 0 · Answer 3 · answered Sep 17 '18 at 15:03

0

If your ToUppercase really cannot return the new string, you might try the following:

ToUppercase(str);
if (str.find("AAA") != string::npos)
{
  ..
}

answered Sep 17 '18 at 15:03

Robert Kock

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Cant use the void func for converting string to Uppercase directly in if statement- c++

3 Answers3