std::string::operator== fails for equal strings?

This is a discussion on std::string::operator== fails for equal strings? within the C++ Programming forums, part of the General Programming Boards category; Hi, in this simple peace of code I compare std::string's for equality: Code: const int UserTypes::getInt(const std::string& str) const throw(NoExistingTypeException) ...

  1. #1
    Registered User
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    std::string::operator== fails for equal strings?

    Hi,

    in this simple peace of code I compare std::string's for equality:

    Code:
    const int
    UserTypes::getInt(const std::string& str) const throw(NoExistingTypeException)
    {
    	for
    	(
    		std::map<int, std::string>::const_iterator citer = mUserTypesMap.begin();
    		citer != mUserTypesMap.end();
    		++citer
    	)
    	{
    		if(citer->second == str)
    		{
    			return citer->first;
    		}
    	}
    	
    	throw NoExistingTypeException();
    }
    I've checked the values of the two compared strings inside the debugger. They are 100% equal (or I got crazy somehow) but the operator returns false. I guess I'm doing something really stupid but I'm unable to see what this morning.
    Thank you in advance!

  2. #2
    Kernel hacker
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    I doubt they are identical. Are you sure you are not missing some unprintable last character on one side or the other. Are the lengths the same?

    --
    Mats
    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

  3. #3
    C++まいる!Cをこわせ! Elysia's Avatar
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    They can't be equal if operator == fails.
    Check for case error, mismatches characterd (I and l maybe?), and hidden characters.
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

  4. #4
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    You are right, one of the strings had an additional character (0x00) appended. Thanks

  5. #5
    Captain Crash brewbuck's Avatar
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    Quote Originally Posted by pheres View Post
    You are right, one of the strings had an additional character (0x00) appended. Thanks
    A great piece of evidence that std::string is not a null-terminated format. The presence of the null terminator made a difference.

    I suspect that some piece of code which converts from C-style string to std::string is erroneously including the null terminator in the total count.

  6. #6
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    Exactly. I wrongly passed strlen(char_array)+1 to the string-constructor somethere. C-strings are a bit confusing sometimes if one is not used to them and has to interface some c-api from time to time.

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