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CString and GetLength

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I ran into this problem recently when debugging some native code and thought that it will be good to share this with everyone.

CString sampleString = CString(_T("Sample\0String"), 14);

int len = sampleString.GetLength(); // len is 14

CString trimmedString = sampleString.Trim(); // trimmedString = "Sample"

CString newstring = CString(sampleString); // newString = "Sample"

len = newstring.GetLength(); // len = 14

CString GetLength returns the length that you passed to it in the constructor and not the length of the string. This can be confusing if you copy the string and loop through the length. It can also be the cause of bugs is you get the length and use CString.GetBuffer() and loop through the buffer for the length.

It looks like CString.GetLength() is the size of the internal buffer and nothing more.

 

MSDN documentation for CString - https://msdn.microsoft.com/en-us/library/aa300471(VS.60).aspx

Comments

  • Anonymous
    February 06, 2009
    PingBack from http://www.clickandsolve.com/?p=4610

  • Anonymous
    February 06, 2009
    Nice post. Where is CString.Trim() in MSDN? Is it typo of CString.TrimRight()?

  • Anonymous
    February 07, 2009
    Interesting, I could't find it either. But it compiles and works. It is supposed to remove leading and trailing white spaces I would think.

  • Anonymous
    February 26, 2009
    Good one !!! Bro, do you remember me ?

  • Anonymous
    March 05, 2009
    Am I correct to assume that this is a heavy bug? Just tried this code in Visual Studio 2005 and it really behaved as described. I was sure that CString::GetLength() would always return the number of charactes up to the first null terminator (without including it in the count). All my code relies on that assumption...

  • Anonymous
    March 06, 2009
    I would agree. I did not realize this until I ran into this issue recently. The assumption that CString makes may be is that the data in the buffer is not binary and does not contain null terminators in it. But that assumption is not evident from the documentation.

  • Anonymous
    March 11, 2009
    Do you have any plans to officially report this bug to Microsoft? If not, do you know what would be the place to do so on my own? And also in this case, would I be allowed to copy/paste your code from above into this bug report? Thanks, Patrik

  • Anonymous
    March 13, 2009
    Let me try to contact the right owners and see what they have to say. In the mean time feel free to use the code above.

  • Anonymous
    September 27, 2009
    use strlen() I'm pretty sure GetLength can only bu used with assert, like an if statment.

  • Anonymous
    April 28, 2010
    Use ReleaseBuffer for memory modifications that are external to the CString Class.

  • Anonymous
    August 18, 2010
    The comment has been removed

  • Anonymous
    August 18, 2010
    Here we are, msdn.microsoft.com/.../ms174288.aspx "A CString object keeps character data in a CStringData object. CString accepts null-terminated C-style strings, but does not retain the null character in the stored character data. Instead, CString tracks string length. CString does provide a null terminator when it exports a C-style string. You can insert a null character amidst stored character data, but it may produce unexpected results."