free (Free Memory Command)
Description

The free command in VSDebugPro is used to release memory that was previously allocated using the malloc command. This command is crucial for managing memory during debugging sessions, especially when simulating or testing memory allocation scenarios.

Syntax

free <address>
Parameters
  • <address>: The memory address to be freed. This should be an address that was previously returned by the malloc command.
Behavior
  • The free command releases the memory block at the specified address, making it available for future allocations.
  • After freeing, the memory is no longer valid for use in the debugged process.
  • The command does not modify the value of any pointers in the debugged process that may still be pointing to the freed memory.
Important Notes

  1. Only free memory allocated by malloc: Only use free on addresses that were returned by the malloc command in VSDebugPro. Attempting to free other addresses may lead to undefined behavior or crashes.

  2. Double free: Freeing the same memory address twice is an error and may cause instability in the debugged process.

  3. Use-after-free: After freeing memory, any attempts to read from or write to that memory address in the debugged process may result in undefined behavior or crashes.

  4. Pointer updates: The free command does not automatically update or nullify any pointers in your code that may be pointing to the freed memory. It’s your responsibility to manage these pointers in your debugging session.

  5. No return value: The free command doesn’t return a value. Successful execution is indicated by the absence of error messages.

Examples

  1. Free memory at a specific address:

    free 0x00500000

  2. Free memory using a variable that holds the address:

    free myAllocatedPointer
Best Practices
  1. Always pair malloc and free calls to prevent memory leaks.
  2. Keep track of allocated addresses to ensure all allocations are properly freed.
  3. After freeing memory, consider setting any pointers to that memory to NULL in your code to prevent accidental use of freed memory.
  4. Use this command in conjunction with memory analysis tools to detect memory leaks and invalid memory accesses.
Example Workflow

  1. Allocate memory:

    malloc 1024

    Output:

    Allocated: 1024 bytes at address: 0x00500000

  2. Use the allocated memory in your debugging session…

  3. Free the allocated memory:

    free 0x00500000

    Output:

    Released memory at address: 0x00500000
Troubleshooting
  • If you receive an error when trying to free memory, double-check that the address is correct and was obtained from a malloc call.
  • If your debugged process crashes after a free call, check for use-after-free scenarios in your code.
  • If you suspect memory leaks, use memory analysis tools in conjunction with careful use of malloc and free to track allocations and deallocations.
Caution

The free command, like its C/C++ counterpart, is a powerful tool but requires careful use. Improper use can lead to difficult-to-debug issues like heap corruption or use-after-free bugs. Always ensure you’re freeing the correct memory and not using it after freeing.