Matching substr() results

Hey!

I've got a program that... well, check out the code below (what I currently have):

Code:

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if(userInput.substr(0, 3) == 'cd ' || 'Cd ' || 'cD ' || 'CD ')
{
        nDirLoc = userInput.substr(3, 255);
}

---

As you can see, I have an if loop that I want to check to see the first three characters of a string with to see if they match what I had put in.

GCC complains:

Quote:

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no match for 'operator==' in 'std::basic_string<_CharT, _Traits, _Alloc>::substr(typename _Alloc::size_type, typename _Alloc::size_type) const [with _CharT = char, _Traits = std::char_traits<char>, _Alloc = std::allocator<char>](0u, 3u) == 6513696'

---

How can I go about checking to see whether or not the substring results are that of what I am expecting?

Thanks for the help!
FlyingIsFun1217

1) ' delimits character literals, not string literals.

2) || tests completely independent conditions. Your if statement, if it used string literals, would test
if the initial 3 characters of userInput are "cd "
OR
if the string literal "Cd " evaluates to true
OR
if the string literal "cD " evaluates to true
OR
if the string literal "CD " evaluates to true.

You should get some string-to-lower function, apply it to the substring, and simply compare once against "cd ". There's one in Boost. (Or this one.)

Alright, thanks for pointing out the ' and " difference. Guess I was too tired, and forgot to check!

With the string-to-lower function, would that be collecting input, and lowercasing it all?

Thanks again, always very helpful here!
FlyingIsFun1217

Quote:

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Originally Posted by FlyingIsFun1217

Alright, thanks for pointing out the ' and " difference. Guess I was too tired, and forgot to check!

With the string-to-lower function, would that be collecting input, and lowercasing it all?

Thanks again, always very helpful here!
FlyingIsFun1217

---

You don't want to lower-case all of the input, just the command that you need to compare case-insensitively [in fact, you may also use a case-insensitive compare, but that's likely to just lower-case the strign anyways].

The reason you don't just lowercase the whole thing is that some commands may differentiate between options that are upper case and options that are lower-case. gcc for example do not treat -C and -c as the same thing, nor -e and -E or -s and -S. Likewise, it's nice to be able to use mixed case when creating filenames and directory names - even if the OS doesn't make the difference into different files, it's easier to read if the case is "what you expect".

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Mats