Dr. Dobb's Journal - October 2007 - (Page 54) State of the Art LOGGING IN C++ you can change the output from the default stderr to some specific file (error checking/handling omitted for brevity): FILE* pFile = fopen(“application.log”, “a”); Output2FILE::Stream() = pFile; FILE_LOG(logINFO) << ; A note for multithreaded applications: The Output2FILE policy implementation is good if you don’t set the destination of the log concurrently. If, on the other hand, you plan to dynamically change the logging stream at runtime from arbitrary threads, you should use appropriate interlocking using your platform’s threading facilities, or a more portable wrapper such as Boost threads. Listing Three shows how you can do it using Boost threads. Needless to say, interlocked logging will be slower, yet unused logging will run as fast as ever. This is because the test in the macro is unsynchronized—a benign race condition that does no harm, assuming integers are assigned atomically (a fair assumption on most platforms). Listing Two class Output2FILE // implementation of OutputPolicy { public: static FILE*& Stream(); static void Output(const std::string& msg); }; inline FILE*& Output2FILE::Stream() { static FILE* pStream = stderr; return pStream; } inline void Output2FILE::Output(const std::string& msg) { FILE* pStream = Stream(); if (!pStream) return fprintf(pStream, "%s", msg.c_str()); fflush(pStream); } typedef Log FILELog; #define FILE_LOG(level) \ if (level > FILELog::ReportingLevel() || !Output2FILE::Stream()) ; \ else FILELog().Get(messageLevel) Compile-Time Plateau Logging Level Sometimes, you might feel the footprint of the application increased more than you can afford, or that the runtime comparison incurred by even unused logging statements is significant. Let’s provide a means to eliminate some of the logging (at compile time) by using a preprocessor symbol FILELOG_MAX_LEVEL: on-DEBUG4 AVERAGE STDEV 00:00:28.002 0.0000029838 off-INFO 00:00:25.106 0.0000008605 on-INFO 00:00:25.109 0.0000014926 Table 1 54 Dr. Dobb’s Journal l www.ddj.com l October 2007 http://www.xoreax.com http://www.abxsoft.com http://www.xoreax.com http://www.ddj.com
Table of Contents Feed for the Digital Edition of Dr. Dobb's Journal - October 2007 Cover Contents Hmmmm Alia Vox Developer Diaries Developer’s Notebook AI: It’s OK Again! Conversations Visual Cryptography and Bit-Plane Complexity Segmentation Inside the Windows Vista Disk Encryption Algorithm Memory-Aware Components Software and the Core Description Process Logging In C++ Effective Concurrency The Agile Edge Swaine’s Flames Dr. Dobb's Journal - October 2007 Dr. Dobb's Journal - October 2007 - Cover (Page Cover1) Dr. Dobb's Journal - October 2007 - Cover (Page Cover2) Dr. Dobb's Journal - October 2007 - Cover (Page 1) Dr. Dobb's Journal - October 2007 - Cover (Page 2) Dr. Dobb's Journal - October 2007 - Cover (Page 3) Dr. Dobb's Journal - October 2007 - Contents (Page 4) Dr. Dobb's Journal - October 2007 - Contents (Page 5) Dr. Dobb's Journal - October 2007 - Hmmmm (Page 6) Dr. Dobb's Journal - October 2007 - Hmmmm (Page 7) Dr. Dobb's Journal - October 2007 - Hmmmm (Page 8) Dr. Dobb's Journal - October 2007 - Hmmmm (Page 9) Dr. Dobb's Journal - October 2007 - Alia Vox (Page 10) Dr. Dobb's Journal - October 2007 - Alia Vox (Page 11) Dr. Dobb's Journal - October 2007 - Developer Diaries (Page 12) Dr. Dobb's Journal - October 2007 - Developer Diaries (Page 13) Dr. Dobb's Journal - October 2007 - Developer’s Notebook (Page 14) Dr. Dobb's Journal - October 2007 - Developer’s Notebook (Page 15) Dr. Dobb's Journal - October 2007 - AI: It’s OK Again! (Page 16) Dr. Dobb's Journal - October 2007 - AI: It’s OK Again! (Page 17) Dr. Dobb's Journal - October 2007 - AI: It’s OK Again! (Page 18) Dr. Dobb's Journal - October 2007 - AI: It’s OK Again! (Page 19) Dr. Dobb's Journal - October 2007 - Conversations (Page 20) Dr. Dobb's Journal - October 2007 - Conversations (Page 21) Dr. Dobb's Journal - October 2007 - Visual Cryptography and Bit-Plane Complexity Segmentation (Page 22) Dr. Dobb's Journal - October 2007 - Visual Cryptography and Bit-Plane Complexity Segmentation (Page 23) Dr. Dobb's Journal - October 2007 - Visual Cryptography and Bit-Plane Complexity Segmentation (Page 24) Dr. Dobb's Journal - October 2007 - Visual Cryptography and Bit-Plane Complexity Segmentation (Page 25) Dr. Dobb's Journal - October 2007 - Visual Cryptography and Bit-Plane Complexity Segmentation (Page 26) Dr. Dobb's Journal - October 2007 - Visual Cryptography and Bit-Plane Complexity Segmentation (Page 27) Dr. Dobb's Journal - October 2007 - Visual Cryptography and Bit-Plane Complexity Segmentation (Page 28) Dr. Dobb's Journal - October 2007 - Visual Cryptography and Bit-Plane Complexity Segmentation (Page 29) Dr. Dobb's Journal - October 2007 - Inside the Windows Vista Disk Encryption Algorithm (Page 30) Dr. Dobb's Journal - October 2007 - Inside the Windows Vista Disk Encryption Algorithm (Page 31) Dr. Dobb's Journal - October 2007 - Inside the Windows Vista Disk Encryption Algorithm (Page 32) Dr. Dobb's Journal - October 2007 - Inside the Windows Vista Disk Encryption Algorithm (Page 33) Dr. Dobb's Journal - October 2007 - Memory-Aware Components (Page 34) Dr. Dobb's Journal - October 2007 - Memory-Aware Components (Page 35) Dr. Dobb's Journal - October 2007 - Memory-Aware Components (Page 36) Dr. Dobb's Journal - October 2007 - Memory-Aware Components (Page 37) Dr. Dobb's Journal - October 2007 - Memory-Aware Components (Page 38) Dr. Dobb's Journal - October 2007 - Memory-Aware Components (Page 39) Dr. Dobb's Journal - October 2007 - Memory-Aware Components (Page 40) Dr. Dobb's Journal - October 2007 - Memory-Aware Components (Page 41) Dr. Dobb's Journal - October 2007 - Software and the Core Description Process (Page 42) Dr. Dobb's Journal - October 2007 - Software and the Core Description Process (Page 43) Dr. Dobb's Journal - October 2007 - Software and the Core Description Process (Page 44) Dr. Dobb's Journal - October 2007 - Software and the Core Description Process (Page 45) Dr. Dobb's Journal - October 2007 - Software and the Core Description Process (Page 46) Dr. Dobb's Journal - October 2007 - Software and the Core Description Process (Page 47) Dr. Dobb's Journal - October 2007 - Software and the Core Description Process (Page 48) Dr. Dobb's Journal - October 2007 - Software and the Core Description Process (Page 49) Dr. Dobb's Journal - October 2007 - Logging In C++ (Page 50) Dr. Dobb's Journal - October 2007 - Logging In C++ (Page 51) Dr. Dobb's Journal - October 2007 - Logging In C++ (Page 52) Dr. Dobb's Journal - October 2007 - Logging In C++ (Page 53) Dr. Dobb's Journal - October 2007 - Logging In C++ (Page 54) Dr. Dobb's Journal - October 2007 - Logging In C++ (Page 55) Dr. Dobb's Journal - October 2007 - Logging In C++ (Page 56) Dr. Dobb's Journal - October 2007 - Effective Concurrency (Page 57) Dr. Dobb's Journal - October 2007 - Effective Concurrency (Page 58) Dr. Dobb's Journal - October 2007 - Effective Concurrency (Page 59) Dr. Dobb's Journal - October 2007 - The Agile Edge (Page 60) Dr. Dobb's Journal - October 2007 - The Agile Edge (Page 61) Dr. Dobb's Journal - October 2007 - The Agile Edge (Page 62) Dr. Dobb's Journal - October 2007 - The Agile Edge (Page 63) Dr. Dobb's Journal - October 2007 - Swaine’s Flames (Page 64) Dr. Dobb's Journal - October 2007 - Swaine’s Flames (Page Cover3) Dr. Dobb's Journal - October 2007 - Swaine’s Flames (Page Cover4)
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