Dont understand error message

This is a discussion on Dont understand error message within the C++ Programming forums, part of the General Programming Boards category; I get an error message on the second line and I dont understand why. Shouldnt this code compile? Code: wstring ...

  1. #1
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    Dont understand error message

    I get an error message on the second line and I dont understand why. Shouldnt this code compile?

    Code:
    wstring s(FileName, FileNameLength);
    s = wstring(L"\\") + s;
    the message is:

    1>d:\dev\projects\dirwatcher\dirwatcher\dirwatcher .cpp(27) : error C2784: 'std::_String_iterator<_Elem,_Traits,_Alloc> std:perator +(_String_iterator<_Elem,_Traits,_Alloc>::differen ce_type,std::_String_iterator<_Elem,_Traits,_Alloc >)' : could not deduce template argument for 'std::_String_iterator<_Elem,_Traits,_Alloc>' from 'std::wstring'

  2. #2
    Kernel hacker
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    Did you include <string>?

    --
    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
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    lol that was the problem. been a while since I didnt understand such a basic issue. Strange though that it did work when I rewrote it to the following without including string either.

    Code:
    wstring temp;
    wstring s(fni.FileName, fni.FileNameLength);
    temp += wstring(Dir);
    temp += L"\\";
    temp += s;

  4. #4
    Cat without Hat CornedBee's Avatar
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    That's because += is a member of std::basic_string and thus available when an internal component of the MS library include <xstring>, whereas + is a free function defined in <string>, and thus not available.
    All the buzzt!
    CornedBee

    "There is not now, nor has there ever been, nor will there ever be, any programming language in which it is the least bit difficult to write bad code."
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  5. #5
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    Quote Originally Posted by CornedBee View Post
    That's because += is a member of std::basic_string and thus available when an internal component of the MS library include <xstring>, whereas + is a free function defined in <string>, and thus not available.
    And this implies that <xstring> gets included by some other component at some point or another - you STILL SHOULD include <string> since you are using std:w)string - it may work as it is, but it's a bad idea to rely on it, as a different set of include files may drag in less "extras" and thus break your build.

    --
    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.

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