Why is this string reversal C code causing a segmentation fault? [duplicate]

Answer 1

Which compiler and debugger are you using? Using gcc and gdb, I would compile the code with -g flag and then run it in gdb. When it segfaults, I would just do a backtrace (bt command in gdb) and see which is the offending line causing the problem. Additionally, I would just run the code step by step, while "watching" the pointer values in gdb and know where exactly is the problem.

Good luck.

Answer 2

You code could be segfaulting for a number of reasons. Here are the ones that come to mind

1. s is NULL
2. s points to a const string which is held in read only memory
3. s is not NULL terminated

I think #2 is the most likely. Can you show us the call site of reverse?

EDIT

Based on your sample #2 is definitely the answer. A string literal in C/C++ is not modifiable. The proper type is actually const char* and not char*. What you need to do is pass a modifiable string into that buffer.

Quick example:

char* pStr = strdup("foobar");
reverse(pStr);
free(pStr);