ctypes return a string from c function

Question

I\'m a Python veteran, but haven\'t dabbled much in C. After half a day of not finding anything on the internet that works for me, I thought I would ask here and get the hel

Answer 1

Here's what happens. And why it's breaking. When hello() is called, the C stack pointer is moved up, making room for any memory needed by your function. Along with some function call overhead, all of your function locals are managed there. So that static char greeting[100], means that 100 bytes of the increased stack are for that string. You than use some functions that manipulate that memory. At the you place a pointer on the stack to the greeting memory. And then you return from the call, at which point, the stack pointer is retracted back to it's original before call position. So those 100 bytes that were on the stack for the duration of your call, are essentially up for grabs again as the stack is further manipulated. Including the address field which pointed to that value and that you returned. At that point, who knows what happens to it, but it's likely set to zero or some other value. And when you try to access it as if it were still viable memory, you get a segfault.

To get around, you need to manage that memory differently somehow. You can have your function allocate the memory on the heap, but you'll need to make sure it gets free()'ed at a later date, by your binding. OR, you can write your function so that the binding language passes it a glump of memory to be used.