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C/C++ Debugging Tips

C/C++-SPECIFIC GUIDANCE:

Prerequisites:

  • Use C/C++ extension for VS Code (by Microsoft)
  • Ensure GDB or LLDB debugger is installed
  • Compile with debug symbols (-g flag)
  • Set breakpoints in .c, .cpp, .cc, .h, .hpp files
  • Use 'cppdbg' debug configuration type

C/C++-Specific Best Practices:

  • Compilation: Always compile with -g flag and disable optimizations (-O0) for debugging
  • Memory Issues: Watch for buffer overflows, memory leaks, and dangling pointers
  • Pointers: Carefully inspect pointer values and dereferenced contents
  • Stack Frames: Use call stack to trace function calls and local variables
  • Core Dumps: Enable core dumps for post-mortem debugging of crashes

Common C++ Debug Configurations:

GDB (Linux/Windows with MinGW):

{
    "type": "cppdbg",
    "request": "launch",
    "name": "Debug with GDB",
    "program": "${fileDirname}/${fileBasenameNoExtension}",
    "args": [],
    "stopAtEntry": false,
    "cwd": "${fileDirname}",
    "environment": [],
    "externalConsole": false,
    "MIMode": "gdb",
    "setupCommands": [
        {
            "description": "Enable pretty-printing for gdb",
            "text": "-enable-pretty-printing",
            "ignoreFailures": true
        }
    ]
}

LLDB (macOS):

{
    "type": "cppdbg",
    "request": "launch",
    "name": "Debug with LLDB",
    "program": "${fileDirname}/${fileBasenameNoExtension}",
    "args": [],
    "stopAtEntry": false,
    "cwd": "${fileDirname}",
    "environment": [],
    "externalConsole": false,
    "MIMode": "lldb"
}

Debugging Tips:

  • Use printf() or std::cout for quick debugging
  • Watch for uninitialized variables
  • Check array bounds carefully
  • Be aware of undefined behavior from pointer arithmetic
  • Use address sanitizer (-fsanitize=address) to detect memory errors
  • Use valgrind for memory leak detection (Linux)

Common Issues:

  • "Unable to start debugging": Ensure executable is compiled with debug symbols
  • "No symbol table": Recompile with -g flag
  • Breakpoints grayed out: Source file doesn't match compiled binary - rebuild
  • Segmentation fault: Use backtrace to find the crashing line, check pointer operations
  • Optimized away variables: Compile with -O0 to disable optimizations

Memory Debugging:

  • Valgrind: valgrind --leak-check=full ./program
  • Address Sanitizer: Compile with -fsanitize=address -fno-omit-frame-pointer
  • Watch expressions: Monitor pointer values and array indices during stepping