Workaround for IShellLink::GetPath()
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Workaround for IShellLink::GetPath(), which sometimes fails and crashes the application.
Introduction
IShellLink::GetPath() may fail and crash your application. This is a workaround to help you out of this.
Using the code
This is the straight forward implementation://***************************************************************************** // File ..................: ReadLnkFile.cpp // Description ...........: Decoder for .lnk files on WINDOWS // Author ................: Peter Thoemmes (http://www.notes-about-cpp.com/) //----------------------------------------------------------------------------- // # !!! Disclaimer !!! # // # This source code is provided "AS-IS" basis, without any warranties or # // # representations express, implied or statutory; including, without # // # limitation, warranties of quality, performance, non-infringement, # // # merchantability or fitness for a particular purpose. Peter Thoemmes # // # does not warrant that this source code will meet your needs or be free # // # from errors. # //----------------------------------------------------------------------------- // Many thanks to Jesse Hager (jessehager@iname.com) for reverse engineering // the shortcut file format and publishing the document 'The Windows Shortcut // File Format'. //----------------------------------------------------------------------------- // Copyright (c) 2008 Peter Thoemmes, Weinbergstr. 3a, D-54441 Ockfen/Germany //***************************************************************************** #include <string> #include <vector> using namespace std; //----------------------------------------------------------------------------- // Get target file (full local path) from a link file (.lnk): //----------------------------------------------------------------------------- string ReadLnkFile(const string& strFullLinkFileName) { //------------------------------------------------------------------------- // How to read the target's path from a .lnk-file: //------------------------------------------------------------------------- // Problem: // // The COM interface to shell32.dll IShellLink::GetPath() fails! // // Solution: // // We need to parse the file manually. The path can be found like shown // here, if the shell item id list is present. In case it is not present // we have to assume A = -6, but not to parse/decode byte 76 and 77. // // +---------------------+-----------------------------------------------+ // | Index | Description | // +---------------------+-----------------------------------------------+ // | 0 | 'L' (magic value) | // +---------------------+-----------------------------------------------+ // | ... | ... | // +---------------------+-----------------------------------------------+ // | 76 | A_0 | // +---------------------+-----------------------------------------------+ // | 77 | A_1 (16 bit) [w/o shell item id list: A = -6] | // +---------------------+-----------------------------------------------+ // | ... | ... | // +---------------------+-----------------------------------------------+ // | 78 + 16 + A | B_0 | // +---------------------+-----------------------------------------------+ // | 78 + 16 + A + 1 | B_1 | // +---------------------+-----------------------------------------------+ // | 78 + 16 + A + 2 | B_2 | // +---------------------+-----------------------------------------------+ // | 78 + 16 + A + 3 | B_3 (32 bit) | // +---------------------+-----------------------------------------------+ // | ... | ... | // +---------------------+-----------------------------------------------+ // | 78 + A + B | PATH_STR_0 | // +---------------------+-----------------------------------------------+ // | 78 + A + B + 1 | PATH_STR_1 | // +---------------------+-----------------------------------------------+ // | 78 + A + B + 2 | PATH_STR_2 | // +---------------------+-----------------------------------------------+ // | ... | ... | // +---------------------+-----------------------------------------------+ // | ... | 0x00 | // +---------------------+-----------------------------------------------+ //------------------------------------------------------------------------- //------------------------------------------------------------------------- // Get the .lnk-file content: //------------------------------------------------------------------------- FILE* pFile = fopen(strFullLinkFileName.c_str(),"rb"); if(!pFile) return string(""); vector<unsigned char> vectBuffer; unsigned char byte = '?'; while((byte = (unsigned char) fgetc(pFile)) != (unsigned char) EOF) vectBuffer.push_back(byte); fclose(pFile); //------------------------------------------------------------------------- // Check the magic value (first byte) and the GUID (16 byte from 5th byte): //------------------------------------------------------------------------- // The GUID is telling the version of the .lnk-file format. We expect the // following GUID (HEX): 01 14 02 00 00 00 00 00 C0 00 00 00 00 00 00 46. //------------------------------------------------------------------------- if(vectBuffer.size() < 20) return string(""); if(vectBuffer[0] != (unsigned char) 'L') //test the magic value return string(""); if((vectBuffer[4] != 0x01) || //test the GUID (vectBuffer[5] != 0x14) || (vectBuffer[6] != 0x02) || (vectBuffer[7] != 0x00) || (vectBuffer[8] != 0x00) || (vectBuffer[9] != 0x00) || (vectBuffer[10] != 0x00) || (vectBuffer[11] != 0x00) || (vectBuffer[12] != 0xC0) || (vectBuffer[13] != 0x00) || (vectBuffer[14] != 0x00) || (vectBuffer[15] != 0x00) || (vectBuffer[16] != 0x00) || (vectBuffer[17] != 0x00) || (vectBuffer[18] != 0x00) || (vectBuffer[19] != 0x46)) { return string(""); } //------------------------------------------------------------------------- // Get the flags (4 byte from 21st byte): //------------------------------------------------------------------------- // Check if it points to a file or directory! //------------------------------------------------------------------------- // Flags (4 byte little endian): // Bit 0 -> has shell item id list // Bit 1 -> points to file or directory // Bit 2 -> has description // Bit 3 -> has relative path // Bit 4 -> has working directory // Bit 5 -> has commandline arguments // Bit 6 -> has custom icon //------------------------------------------------------------------------- unsigned int i = 20; if(vectBuffer.size() < (i + 4)) return string(""); unsigned int dwFlags = (unsigned int) vectBuffer[i]; //little endian format dwFlags |= (((unsigned int) vectBuffer[++i]) << 8); dwFlags |= (((unsigned int) vectBuffer[++i]) << 16); dwFlags |= (((unsigned int) vectBuffer[++i]) << 24); bool bHasShellItemIdList = (dwFlags & 0x00000001) ? true : false; bool bPointsToFileOrDir = (dwFlags & 0x00000002) ? true : false; if(!bPointsToFileOrDir) return string(""); //------------------------------------------------------------------------- // Shell item id list (starts at 76 with 2 byte length -> so we can skip): //------------------------------------------------------------------------- int32 A = -6; if(bHasShellItemIdList) { i = 76; if(vectBuffer.size() < (i + 2)) return string(""); A = (unsigned char) vectBuffer[i]; //little endian format A |= (((unsigned char) vectBuffer[++i]) << 8); } //------------------------------------------------------------------------- // File location info: //------------------------------------------------------------------------- // Follows the shell item id list and starts with 4 byte structure length, // followed by 4 byte offset for skipping. //------------------------------------------------------------------------- i = 78 + 4 + A; if(vectBuffer.size() < (i + 4)) return string(""); unsigned int B = (unsigned int) vectBuffer[i]; //little endian format B |= (((unsigned int) vectBuffer[++i]) << 8); B |= (((unsigned int) vectBuffer[++i]) << 16); B |= (((unsigned int) vectBuffer[++i]) << 24); //------------------------------------------------------------------------- // Local volume table: //------------------------------------------------------------------------- // Follows the file location info and starts with 4 byte table length for // skipping the actual table and moving to the local path string. //------------------------------------------------------------------------- i = 78 + A + B; if(vectBuffer.size() < (i + 4)) return string(""); unsigned int C = (unsigned int) vectBuffer[i]; //little endian format C |= (((unsigned int) vectBuffer[++i]) << 8); C |= (((unsigned int) vectBuffer[++i]) << 16); C |= (((unsigned int) vectBuffer[++i]) << 24); //------------------------------------------------------------------------- // Local path string (ending with 0x00): //------------------------------------------------------------------------- i = 78 + A + B + C; if(vectBuffer.size() < (i + 1)) return string(""); string strLinkedTarget = ""; for(;i < vectBuffer.size();++i) { strLinkedTarget.append(1,(char) vectBuffer[i]); if(!vectBuffer[i]) break; } //Return if empty: if(strLinkedTarget.empty()) return string(""); //------------------------------------------------------------------------- // Convert the target path into the long format (format without ~): //------------------------------------------------------------------------- // GetLongPathNameA() fails it the target file doesn't exist! //------------------------------------------------------------------------- char* szLinkedTargetLongFormat = new char[MAX_PATH + 1]; if(!szLinkedTargetLongFormat) return string(""); if(!::GetLongPathNameA( strLinkedTarget.c_str(), szLinkedTargetLongFormat, MAX_PATH)) { return strLinkedTarget; //file doesn't exist } string strLinkedTargetLongFormat(szLinkedTargetLongFormat); delete[] szLinkedTargetLongFormat; return strLinkedTargetLongFormat; }
Simply call the function ReadLnkFile() to get your target file from the .lnk file:
string strFullTargetPath = ReadLnkFile("C:\\MyShortcut.lnk");
Points of Interest
Many thanks to Jesse Hager (jessehager@iname.com) for reverse engineering the shortcut file format and publishing the document 'The Windows Shortcut File Format'. Without this I would still stuck with IShellLink::GetPath() crashing my application.
History
2008-02-29, Peter Thoemmes: first release.
2008-03-01, Peter Thoemmes: description updated.