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Byte Order Macros — a portable way to convert between different byte orders.
#include <glib.h> #define G_BYTE_ORDER #define G_LITTLE_ENDIAN #define G_BIG_ENDIAN #define G_PDP_ENDIAN #define g_htonl (val) #define g_htons (val) #define g_ntohl (val) #define g_ntohs (val) #define GINT_FROM_BE (val) #define GINT_FROM_LE (val) #define GINT_TO_BE (val) #define GINT_TO_LE (val) #define GUINT_FROM_BE (val) #define GUINT_FROM_LE (val) #define GUINT_TO_BE (val) #define GUINT_TO_LE (val) #define GLONG_FROM_BE (val) #define GLONG_FROM_LE (val) #define GLONG_TO_BE (val) #define GLONG_TO_LE (val) #define GULONG_FROM_BE (val) #define GULONG_FROM_LE (val) #define GULONG_TO_BE (val) #define GULONG_TO_LE (val) #define GINT16_FROM_BE (val) #define GINT16_FROM_LE (val) #define GINT16_TO_BE (val) #define GINT16_TO_LE (val) #define GUINT16_FROM_BE (val) #define GUINT16_FROM_LE (val) #define GUINT16_TO_BE (val) #define GUINT16_TO_LE (val) #define GINT32_FROM_BE (val) #define GINT32_FROM_LE (val) #define GINT32_TO_BE (val) #define GINT32_TO_LE (val) #define GUINT32_FROM_BE (val) #define GUINT32_FROM_LE (val) #define GUINT32_TO_BE (val) #define GUINT32_TO_LE (val) #define GINT64_FROM_BE (val) #define GINT64_FROM_LE (val) #define GINT64_TO_BE (val) #define GINT64_TO_LE (val) #define GUINT64_FROM_BE (val) #define GUINT64_FROM_LE (val) #define GUINT64_TO_BE (val) #define GUINT64_TO_LE (val) #define GUINT16_SWAP_BE_PDP (val) #define GUINT16_SWAP_LE_BE (val) #define GUINT16_SWAP_LE_PDP (val) #define GUINT32_SWAP_BE_PDP (val) #define GUINT32_SWAP_LE_BE (val) #define GUINT32_SWAP_LE_PDP (val) #define GUINT64_SWAP_LE_BE (val)
These macros provide a portable way to determine the host byte order and to convert values between different byte orders.
The byte order is the order in which bytes are stored to create larger data types such as the gint and glong values. The host byte order is the byte order used on the current machine.
Some processors store the most significant bytes (i.e. the bytes that hold the largest part of the value) first. These are known as big-endian processors.
Other processors (notably the x86 family) store the most significant byte last. These are known as little-endian processors.
Finally, to complicate matters, some other processors store the bytes in a rather curious order known as PDP-endian. For a 4-byte word, the 3rd most significant byte is stored first, then the 4th, then the 1st and finally the 2nd.
Obviously there is a problem when these different processors communicate with each other, for example over networks or by using binary file formats. This is where these macros come in. They are typically used to convert values into a byte order which has been agreed on for use when communicating between different processors. The Internet uses what is known as 'network byte order' as the standard byte order (which is in fact the big-endian byte order).
#define G_BYTE_ORDER G_LITTLE_ENDIAN
The host byte order. This can be either G_LITTLE_ENDIAN or G_BIG_ENDIAN (support for G_PDP_ENDIAN may be added in future.)
#define G_LITTLE_ENDIAN 1234
Specifies one of the possible types of byte order. See G_BYTE_ORDER.
#define G_BIG_ENDIAN 4321
Specifies one of the possible types of byte order. See G_BYTE_ORDER.
#define G_PDP_ENDIAN 3412 /* unused, need specific PDP check */
Specifies one of the possible types of byte order (currently unused). See G_BYTE_ORDER.
#define g_htonl(val)
Converts a 32-bit integer value from host to network byte order.
| val : | a 32-bit integer value in host byte order.
nteger value from host to network byte order.
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