How to debug a crashing C++ program?

Methods for debugging C++ crashing programs include: using compiler options to generate debuggable code; using the GDB debugger to step into, inspect variables, set breakpoints, and view stack traces; add assertions to ensure conditions are valid; log events and Error to identify pre-crash exceptions.

#How to debug a crashing C++ program?

When a C++ program crashes, the process of determining the cause of the crash and fixing it is called debugging. Here are some common techniques for debugging C++ crashing programs:

1. Use compiler options

Use compiler options (such as -g## in g++ # flag) compiles the code to generate an executable file containing debugging information. This allows using a debugger (such as GDB) to attach to a running program and step into it.

2. GDB debugger

GDB is a powerful command line debugger that can be used to debug C++ programs. Using GDB you can:

Step through code
• Inspect variables and memory
• Set breakpoints
• View stack traces

3. Assertions

Assertions are checks in a program that ensure that certain conditions are true. If the condition is false, the program will break unexpectedly. This helps identify errors or invalid input in the program.

4. Logging

Logging involves writing program events or error information to a file. By examining log files, you can identify unusual conditions or errors before a program crashes.

Practical Example

Consider the following crashing C++ program:

#include <iostream>

int main() {
  int* ptr = new int;
  *ptr = 10;
  delete ptr;
  *ptr = 20;  // 访问已释放的内存
  return 0;
}

Compiling and running this program will result in a segfault. Using GDB, we can debug the program as follows:

$ gdb ./a.out
(gdb) run
Starting program: /path/to/a.out
[New Thread 15676.0x1153570]
[New Thread 15677.0x1154ec0]

Program received signal SIGSEGV, Segmentation fault.
0x0000555555555527 in main () at main.cpp:9
9           *ptr = 20;  // 访问已释放的内存
(gdb) bt
#0  0x0000555555555527 in main () at main.cpp:9
#1  0x00007ffff7dc36860 in __libc_start_main (main=0x5555555554e0 <main>, argc=1, argv=0x7fffffffdde8, init=<optimized out>, fini=<optimized out>, rtld_fini=<optimized out>, stack_end=0x7fffffffddea) at ../csu/libc-start.c:270

The stack trace indicates that the crash occurs on line 9, which attempts to access freed memory. By examining the previous lines of the program, we can identify the memory management error that caused the crash.

Other Tips

Use a memory debugging tool such as Valgrind or AddressSanitizer to detect memory errors.
• Use a code coverage tool (such as gcov) to identify code paths that were not executed.
• Use breakpoints and logging to gradually narrow down the source of the crash.

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