GetBufferSetLength后需要ReleaseBuffer吗

DrSmart 2011-06-10 09:06:25
GetBufferSetLength后需要ReleaseBuffer吗?比如

CString test="China";
test.GetBufferSetLength(3); 返回应该是Chi,这样的话,是否需要ReleaseBuffer吗? 我知道GetBuffer后需要,
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MagicFuzzX 2011-06-12
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最好都realse下吧
MagicFuzzX 2011-06-12
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GetBuffer修改了缓冲区的数据就要Realse下,要是没修改的话不需要Realse
信阳毛尖 2011-06-12
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调用了GetBuffer或者GetBufferSetLength方法并且修改了缓冲区里的内容之后,如果要调用其它的方法,就要先调用ReleaseBuffer或者ReleaseBufferSetLength方法
kyotrue 2011-06-11
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不管是GetBufferSetLength还是GetBuffer,完了都必须要ReleaseBuffer。
DrSmart 2011-06-10
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晕,楼上有分歧,算了,我还是用Mid吧,就我这个情况,接下来test的不会变,如果用GetBufferSetLength到底用不用release啊,直接说明白,我也会google,就求真相
wocow3 2011-06-10
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CString有个成员专门保存了字符串的长度,所以一旦你直接操作并修改了字符串缓冲区,就必须调用ReleaseBuffer重新计算字符串长度更新这个成员
zyrr159487 2011-06-10
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LS说的很清楚了
Dreadnought 2011-06-10
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The address returned by GetBufferSetLength may not be valid after the call to ReleaseBuffer since additional CString operations may cause the CString buffer to be reallocated.

http://msdn.microsoft.com/en-us/library/aa300459(v=vs.60).aspx
hurryboylqs 2011-06-10
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需要ReleaseBuffer
GetBuffer不一定需要,只要你不修改缓冲区数据
Eleven 2011-06-10
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If you use the pointer returned by GetBufferSetLength to change the string contents, you may need to call ReleaseBuffer before using any other CSimpleStringT member methods.

The address returned by GetBufferSetLength may not be valid after the call to ReleaseBuffer because additional CSimpleStringT operations can cause the CSimpleStringT buffer to be reallocated. The buffer is not reassigned if you do not change the length of the CSimpleStringT.
// ============================================================================= // FILE: StdString.h // AUTHOR: Joe O'Leary (with outside help noted in comments) // // If you find any bugs in this code, please let me know: // // jmoleary@earthlink.net // http://www.joeo.net/stdstring.htm (a bit outdated) // // The latest version of this code should always be available at the // following link: // // http://www.joeo.net/code/StdString.zip (Dec 6, 2003) // // // REMARKS: // This header file declares the CStdStr template. This template derives // the Standard C++ Library basic_string<> template and add to it the // the following conveniences: // - The full MFC CString set of functions (including implicit cast) // - writing to/reading from COM IStream interfaces // - Functional objects for use in STL algorithms // // From this template, we intstantiate two classes: CStdStringA and // CStdStringW. The name "CStdString" is just a #define of one of these, // based upone the UNICODE macro setting // // This header also declares our own version of the MFC/ATL UNICODE-MBCS // conversion macros. Our version looks exactly like the Microsoft's to // facilitate portability. // // NOTE: // If you you use this in an MFC or ATL build, you should include either // afx.h or atlbase.h first, as appropriate. // // PEOPLE WHO HAVE CONTRIBUTED TO THIS CLASS: // // Several people have helped me iron out problems and othewise improve // this class. OK, this is a long list but in my own defense, this code // has undergone two major rewrites. Many of the improvements became // necessary after I rewrote the code as a template. Others helped me // improve the CString facade. // // Anyway, these people are (in chronological order): // // - Pete the Plumber (???) // - Julian Selman // - Chris (of Melbsys) // - Dave Plummer // - John C Sipos // - Chris Sells // - Nigel Nunn // - Fan Xia // - Matthew Williams // - Carl Engman // - Mark Zeren // - Craig Watson // - Rich Zuris // - Karim Ratib // - Chris Conti // - Baptiste Lepilleur // - Greg Pickles // - Jim Cline // - Jeff Kohn // - Todd Heckel // - Ullrich Poll?hne // - Joe Vitaterna // - Joe Woodbury // - Aaron (no last name) // - Joldakowski (???) // - Scott Hathaway // - Eric Nitzche // - Pablo Presedo // - Farrokh Nejadlotfi // - Jason Mills // - Igor Kholodov // - Mike Crusader // - John James // - Wang Haifeng // - Tim Dowty // - Arnt Witteveen // - Glen Maynard // - Paul DeMarco // - Bagira (full name?) // - Ronny Schulz // - Jakko Van Hunen // - Charles Godwin // - Henk Demper // - Greg Marr // - Bill Carducci // - Brian Groose // - MKingman // - Don Beusee // // REVISION HISTORY // // 2005-JAN-10 - Thanks to Don Beusee for pointing out the danger in mapping // length-checked formatting functions to non-length-checked // CRT equivalents. Also thanks to him for motivating me to // optimize my implementation of Replace() // // 2004-APR-22 - A big, big thank you to "MKingman" (whoever you are) for // finally spotting a silly little error in StdCodeCvt that // has been causing me (and users of CStdString) problems for // years in some relatively rare conversions. I had reversed // two length arguments. // // 2003-NOV-24 - Thanks to a bunch of people for helping me clean up many // compiler warnings (and yes, even a couple of actual compiler // errors). These include Henk Demper for figuring out how // to make the Intellisense work on with CStdString on VC6, // something I was never able to do. Greg Marr pointed out // a compiler warning about an unreferenced symbol and a // problem with my version of Load in MFC builds. Bill // Carducci took a lot of time with me to help me figure out // why some implementations of the Standard C++ Library were // returning error codes for apparently successful conversions // between ASCII and UNICODE. Finally thanks to Brian Groose // for helping me fix compiler signed unsigned warnings in // several functions. // // 2003-JUL-10 - Thanks to Charles Godwin for making me realize my 'FmtArg' // fixes had inadvertently broken the DLL-export code (which is // normally commented out. I had to move it up higher. Also // this helped me catch a bug in ssicoll that would prevent // compilation, otherwise. // // 2003-MAR-14 - Thanks to Jakko Van Hunen for pointing out a copy-and-paste // bug in one of the overloads of FmtArg. // // 2003-MAR-10 - Thanks to Ronny Schulz for (twice!) sending me some changes // to help CStdString build on SGI and for pointing out an // error in placement of my preprocessor macros for ssfmtmsg. // // 2002-NOV-26 - Thanks to Bagira for pointing out that my implementation of // SpanExcluding was not properly handling the case in which // the string did NOT contain any of the given characters // // 2002-OCT-21 - Many thanks to Paul DeMarco who was invaluable in helping me // get this code working with Borland's free compiler as well // as the Dev-C++ compiler (available free at SourceForge). // // 2002-SEP-13 - Thanks to Glen Maynard who helped me get rid of some loud // but harmless warnings that were showing up on g++. Glen // also pointed out that some pre-declarations of FmtArg<> // specializations were unnecessary (and no good on G++) // // 2002-JUN-26 - Thanks to Arnt Witteveen for pointing out that I was using // static_cast<> in a place in which I should have been using // reinterpret_cast<> (the ctor for unsigned char strings). // That's what happens when I don't unit-test properly! // Arnt also noticed that CString was silently correcting the // 'nCount' argument to Left() and Right() where CStdString was // not (and crashing if it was bad). That is also now fixed! // // 2002-FEB-25 - Thanks to Tim Dowty for pointing out (and giving me the fix // for) a conversion problem with non-ASCII MBCS characters. // CStdString is now used in my favorite commercial MP3 player! // // 2001-DEC-06 - Thanks to Wang Haifeng for spotting a problem in one of the // assignment operators (for _bstr_t) that would cause compiler // errors when refcounting protection was turned off. // // 2001-NOV-27 - Remove calls to operator!= which involve reverse_iterators // due to a conflict with the rel_ops operator!=. Thanks to // John James for pointing this out. // // 2001-OCT-29 - Added a minor range checking fix for the Mid function to // make it as forgiving as CString's version is. Thanks to // Igor Kholodov for noticing this. // - Added a specialization of std::swap for CStdString. Thanks // to Mike Crusader for suggesting this! It's commented out // because you're not supposed to inject your own code into the // 'std' namespace. But if you don't care about that, it's // there if you want it // - Thanks to Jason Mills for catching a case where CString was // more forgiving in the Delete() function than I was. // // 2001-JUN-06 - I was violating the Standard name lookup rules stated // in [14.6.2(3)]. None of the compilers I've tried so // far apparently caught this but HP-UX aCC 3.30 did. The // fix was to add 'this->' prefixes in many places. // Thanks to Farrokh Nejadlotfi for this! // // 2001-APR-27 - StreamLoad was calculating the number of BYTES in one // case, not characters. Thanks to Pablo Presedo for this. // // 2001-FEB-23 - Replace() had a bug which caused infinite loops if the // source string was empty. Fixed thanks to Eric Nitzsche. // // 2001-FEB-23 - Scott Hathaway was a huge help in providing me with the // ability to build CStdString on Sun Unix systems. He // sent me detailed build reports about what works and what // does not. If CStdString compiles on your Unix box, you // can thank Scott for it. // // 2000-DEC-29 - Joldakowski noticed one overload of Insert failed to do a // range check as CString's does. Now fixed -- thanks! // // 2000-NOV-07 - Aaron pointed out that I was calling static member // functions of char_traits via a temporary. This was not // technically wrong, but it was unnecessary and caused // problems for poor old buggy VC5. Thanks Aaron! // // 2000-JUL-11 - Joe Woodbury noted that the CString::Find docs don't match // what the CString::Find code really ends up doing. I was // trying to match the docs. Now I match the CString code // - Joe also caught me truncating strings for GetBuffer() calls // when the supplied length was less than the current length. // // 2000-MAY-25 - Better support for STLPORT's Standard library distribution // - Got rid of the NSP macro - it interfered with Koenig lookup // - Thanks to Joe Woodbury for catching a TrimLeft() bug that // I introduced in January. Empty strings were not getting // trimmed // // 2000-APR-17 - Thanks to Joe Vitaterna for pointing out that ReverseFind // is supposed to be a const function. // // 2000-MAR-07 - Thanks to Ullrich Poll?hne for catching a range bug in one // of the overloads of assign. // // 2000-FEB-01 - You can now use CStdString on the Mac with CodeWarrior! // Thanks to Todd Heckel for helping out with this. // // 2000-JAN-23 - Thanks to Jim Cline for pointing out how I could make the // Trim() function more efficient. // - Thanks to Jeff Kohn for prompting me to find and fix a typo // in one of the addition operators that takes _bstr_t. // - Got rid of the .CPP file - you only need StdString.h now! // // 1999-DEC-22 - Thanks to Greg Pickles for helping me identify a problem // with my implementation of CStdString::FormatV in which // resulting string might not be properly NULL terminated. // // 1999-DEC-06 - Chris Conti pointed yet another basic_string<> assignment // bug that MS has not fixed. CStdString did nothing to fix // it either but it does now! The bug was: create a string // longer than 31 characters, get a pointer to it (via c_str()) // and then assign that pointer to the original string object. // The resulting string would be empty. Not with CStdString! // // 1999-OCT-06 - BufferSet was erasing the string even when it was merely // supposed to shrink it. Fixed. Thanks to Chris Conti. // - Some of the Q172398 fixes were not checking for assignment- // to-self. Fixed. Thanks to Baptiste Lepilleur. // // 1999-AUG-20 - Improved Load() function to be more efficient by using // SizeOfResource(). Thanks to Rich Zuris for this. // - Corrected resource ID constructor, again thanks to Rich. // - Fixed a bug that occurred with UNICODE characters above // the first 255 ANSI ones. Thanks to Craig Watson. // - Added missing overloads of TrimLeft() and TrimRight(). // Thanks to Karim Ratib for pointing them out // // 1999-JUL-21 - Made all calls to GetBuf() with no args check length first. // // 1999-JUL-10 - Improved MFC/ATL independence of conversion macros // - Added SS_NO_REFCOUNT macro to allow you to disable any // reference-counting your basic_string<> impl. may do. // - Improved ReleaseBuffer() to be as forgiving as CString. // Thanks for Fan Xia for helping me find this and to // Matthew Williams for pointing it out directly. // // 1999-JUL-06 - Thanks to Nigel Nunn for catching a very sneaky bug in // ToLower/ToUpper. They should call GetBuf() instead of // data() in order to ensure the changed string buffer is not // reference-counted (in those implementations that refcount). // // 1999-JUL-01 - Added a true CString facade. Now you can use CStdString as // a drop-in replacement for CString. If you find this useful, // you can thank Chris Sells for finally convincing me to give // in and implement it. // - Changed operators << and >> (for MFC CArchive) to serialize // EXACTLY as CString's do. So now you can send a CString out // to a CArchive and later read it in as a CStdString. I have // no idea why you would want to do this but you can. // // 1999-JUN-21 - Changed the CStdString class into the CStdStr template. // - Fixed FormatV() to correctly decrement the loop counter. // This was harmless bug but a bug nevertheless. Thanks to // Chris (of Melbsys) for pointing it out // - Changed Format() to try a normal stack-based array before // using to _alloca(). // - Updated the text conversion macros to properly use code // pages and to fit in better in MFC/ATL builds. In other // words, I copied Microsoft's conversion stuff again. // - Added equivalents of CString::GetBuffer, GetBufferSetLength // - new sscpy() replacement of CStdString::CopyString() // - a Trim() function that combines TrimRight() and TrimLeft(). // // 1999-MAR-13 - Corrected the "NotSpace" functional object to use _istpace() // instead of _isspace() Thanks to Dave Plummer for this. // // 1999-FEB-26 - Removed errant line (left over from testing) that #defined // _MFC_VER. Thanks to John C Sipos for noticing this. // // 1999-FEB-03 - Fixed a bug in a rarely-used overload of operator+() that // caused infinite recursion and stack overflow // - Added member functions to simplify the process of // persisting CStdStrings to/from DCOM IStream interfaces // - Added functional objects (e.g. StdStringLessNoCase) that // allow CStdStrings to be used as keys STL map objects with // case-insensitive comparison // - Added array indexing operators (i.e. operator[]). I // originally assumed that these were unnecessary and would be // inherited from basic_string. However, without them, Visual // C++ complains about ambiguous overloads when you try to use // them. Thanks to Julian Selman to pointing this out. // // 1998-FEB-?? - Added overloads of assign() function to completely account // for Q172398 bug. Thanks to "Pete the Plumber" for this // // 1998-FEB-?? - Initial submission // // COPYRIGHT: // 2002 Joseph M. O'Leary. This code is 100% free. Use it anywhere you // want. Rewrite it, restructure it, whatever. If you can write software // that makes money off of it, good for you. I kinda like capitalism. // Please don't blame me if it causes your $30 billion dollar satellite // explode in orbit. If you redistribute it in any form, I'd appreciate it // if you would leave this notice here. // ============

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