Detailed explanation of C++ function debugging: How to debug problems in functions containing dynamic memory allocation?

When debugging a function containing dynamic memory allocation in C, you can use: Debugger (GDB/LLDB) to check memory allocation/release (valgrind) Assertion exception handling Practical case: Function free_twice Error: Released memory Debugging using GDB , found that the assertion failed, checked the variable value, and determined that the problem was in releasing the released pointer

C Detailed explanation of function debugging: debugging functions containing dynamic memory allocation

In C, dynamic memory allocation is implemented through the new and delete keywords. Debugging such a function can be challenging when memory issues arise. Let’s explore how to effectively debug such functions:

1. Using a debugger

Using a debugger such as GDB or LLDB is an effective way to debug C functions. These tools allow you to step through code, inspect variables, and set breakpoints.

2. Check the allocation and release of memory in the heap

Use tools such as valgrind to check whether memory allocation and release are performed correctly. It can detect memory leaks and other errors.

3. Use assertions

Use assertions to check the preconditions and postconditions of a function. Assertions that fail at runtime will trigger an error and provide details about the problem.

4. Use exception handling

The exception handling mechanism allows functions to throw exceptions when an error is detected. This helps catch unexpected errors and provide valuable error messages.

Practical case: Debugging a function that releases released memory

Consider the following function:

void free_twice(int *ptr) {
  delete ptr;
  delete ptr;  // 再次释放已释放的内存
}

This function is called for the second time A segfault occurs when delete. Debugging this function using GDB:

(gdb) break free_twice
(gdb) run
(gdb) next
(gdb) next
(gdb) next
*** glibc detected *** double free or corruption (!prev): 
    0x00007ffff705be30 ***
(gdb) bt
#0  0x00007ffff69b03e7 in __GI___assert_fail () from /lib/x86_64-linux-gnu/libc.so.6
#1  0x00007ffff69b8e37 in __GI_raise () from /lib/x86_64-linux-gnu/libc.so.6
#2  0x00007ffff69b98bc in abort () from /lib/x86_64-linux-gnu/libc.so.6
#3  0x00007ffff69d1f8b in __libc_message () from /lib/x86_64-linux-gnu/libc.so.6

The debugger shows that the segfault occurs in the __GI___assert_fail function. This indicates that there is an assertion failure, which is exactly what happened in the code we added with assert. By examining the value of the variable in the function, we can determine that the problem is caused by freeing a freed pointer.

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