Question: I am looking into programming the ESP8266 serial-wifi chip. In its SDK examples it makes extensive use of a function called `os_zalloc` where I would expect `malloc`.

Occasionally though, `os_malloc` is used as well. So they do not appear to be identical in function.

Unfortunately there is no documentation. Can anybody make an educated guess from the following header file? 

```
#ifndef __MEM_H__
#define __MEM_H__

//void *pvPortMalloc( size_t xWantedSize );
//void vPortFree( void *pv );
//void *pvPortZalloc(size_t size);

#define os_malloc   pvPortMalloc
#define os_free     vPortFree
#define os_zalloc   pvPortZalloc

#endif

```

Answer: 
Since `os_zalloc` is a macro, and the definition is given in mem.h, a better question to ask would be about what `pvPortZalloc` does.

Given the function names `pvPortMalloc`, `vPortFree` and `pvPortZalloc` it would appear that the OS in use is FreeRTOS (or it's commercially licensed equivalent OpenRTOS), which is documented - although not specifically `pvPortZalloc`, but it would be strange if it was not simply *allocate and zero initialise* - that is for example what it means [here](http://w1.fi/wpa_supplicant/devel/os_8h.html#aa3941c5693466d194ef568dfe2f299e6). The functions are part of the target porting layer for FreeRTOS, and are not normally called by the application level, but I imagine here the macro wrapper is used to access the porting layer code for application user rather than write it twice. 

In an RTOS kernel RTOS aware dynamic memory allocation functions are required to ensure thread safety, although some standard library implementations include thread safety stubs that you implement using the RTOS mutex calls, which is a better method since existing libaries and C++ `new`/`delete` can be more easily used.
I would say "allocate memory and fill with zeros"