How does sbrk() work in C++?

Question

Where can I read about sbrk() in some detail?

How does it exactly work?

In what situations would I want to use sbrk() instead of th

Answer 1

You never want to use sbrk instead of malloc or free. It is non-portable and is typically used only by implementers of the standard C library or in cases where it's not available. It's described pretty well in its man page:

Description

brk() sets the end of the data segment to the value specified by end_data_segment, when that value is reasonable, the system does have enough memory and the process does not exceed its max data size (see setrlimit(2)).

sbrk() increments the program's data space by increment bytes. sbrk() isn't a system call, it is just a C library wrapper. Calling sbrk() with an increment of 0 can be used to find the current location of the program break.

Return Value

On success, brk() returns zero, and sbrk() returns a pointer to the start of the new area. On error, -1 is returned, and errno is set to ENOMEM.

Finally,malloc and free are not cumbersome - they are the standard way to allocate and release memory in C. Even if you want to implement your own memory allocator, it's best to just use malloc and free as the basis - a common approach is to allocate a large chunk at a time with malloc and provide memory allocation from it (this is what suballocators, or pools, usually implement)

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Re the origin of the name sbrk (or its cousin brk), it may have something to do with the fact that the end of the heap is marked by a pointer known as the "break". The heap starts right after the BSS segments and typically grows up towards the stack.