10. Endian Conversion

GM receive events are delivered to the user in network byte order. This enhances the performance of GM programs, but is a minor inconveniece to developers using the GM API. The client must call a special function to convert each field read from the gm_recv_event_t union to host byte order. Neglecting this conversion will result in undefined program behaviour in most cases.

In the absense of automatic checks, endian conversion is typically an error-prone programming task. Therefore, support has been added to GM-1.4 `gm.h' to ensure that no conversion is missing. Note, however, the support is incompatible with the deprecated gm_send()/GM_SENT_EVENT mechanism in GM. All you need to do to activate the checking is add the line

#define GM_STRONG_TYPES 1

before your the line

#include "gm.h"

in your source code to activate this feature(2). Once the feature is activated, the compiler will report errors if any type conversion is missing. The error messages can be a bit cryptic and are platform specific, but they generally indicate some sort of type mismatch.

Endian conversion of fields in receive events from network to host order is achieved with the following functions:

gm_ntohc()

converts 8-bit fields

gm_ntohs()

converts 16-bit fields

gm_ntohc()

converts 32-bit fields

gm_ntohp()

converts pointer-sized fields