请考虑以下结构和功能
typedef struct __attribute__((__packed__)) req_file {
uint32_t start_pos;
uint32_t byte_count;
uint16_t name_len;
} req_file;
void req_file_hton(req_file *d){
d->name_len = htons(d->name_len);
d->start_pos = htonl(d->start_pos);
d->byte_count = htonl(d->byte_count);
}
void req_file_ntoh(req_file *d){
d->name_len = ntohs(d->name_len);
d->start_pos = ntohl(d->start_pos);
d->byte_count = ntohl(d->byte_count);
}
上面的代码对于编写具有许多字段的许多结构很繁琐。我想一次配置结构的名称和字段，并为我生成函数struct_name_hton和struct_name_ntoh。我尝试过使用x宏，但是运气不好。便携式C预处理器解决方案将受到高度赞赏（非C ++）。
答案 0 :(得分：2)
恕我直言，您应该使用原始缓冲区作为输入/输出。与猜测编译器在每个系统上对字段或结构进行排序的方式相比，这要容易得多（并且更安全）。
此外，这将使您可以打包/解压缩数据，而不必担心字节顺序或内存对齐。
此示例代码中的宏是从the facil.io framework header中提取的：
/** Reads an unaligned network ordered byte stream to a 16 bit number. */
#define fio_str2u16(c) \
((uint16_t)(((uint16_t)(((uint8_t *)(c))[0]) << 8) | \
(uint16_t)(((uint8_t *)(c))[1])))
/** Reads an unaligned network ordered byte stream to a 32 bit number. */
#define fio_str2u32(c) \
((uint32_t)(((uint32_t)(((uint8_t *)(c))[0]) << 24) | \
((uint32_t)(((uint8_t *)(c))[1]) << 16) | \
((uint32_t)(((uint8_t *)(c))[2]) << 8) | \
(uint32_t)(((uint8_t *)(c))[3])))
/** Writes a local 16 bit number to an unaligned buffer in network order. */
#define fio_u2str16(buffer, i) \
do { \
((uint8_t *)(buffer))[0] = ((uint16_t)(i) >> 8) & 0xFF; \
((uint8_t *)(buffer))[1] = ((uint16_t)(i)) & 0xFF; \
} while (0);
/** Writes a local 32 bit number to an unaligned buffer in network order. */
#define fio_u2str32(buffer, i) \
do { \
((uint8_t *)(buffer))[0] = ((uint32_t)(i) >> 24) & 0xFF; \
((uint8_t *)(buffer))[1] = ((uint32_t)(i) >> 16) & 0xFF; \
((uint8_t *)(buffer))[2] = ((uint32_t)(i) >> 8) & 0xFF; \
((uint8_t *)(buffer))[3] = ((uint32_t)(i)) & 0xFF; \
} while (0);
void req_file_read(req_file *d, unsigned char * buffer){
d->byte_count = fio_str2u32(buffer);
d->start_pos = fio_str2u32(buffer + 4);
d->name_len = fio_str2u16(buffer + 8);
}
void req_file_write(unsigned char * buffer, req_file *d){
fio_u2str32(buffer, d->byte_count);
fio_u2str32(buffer + 4, d->start_pos);
fio_u2str16(buffer + 8, d->name_len);
}
这使得在任何系统上处理未对齐的内存访问以及网络字节顺序变得容易得多。基于二进制的数学使这既可移植又节省空间。
根据Lightness Races在Orbit中提出的评论和关注，这是一个带有X宏的标头文件，可用于自动创建X_read / X_write内联函数。
序列化的缺点是，在使用宏声明结构时，应提供原始缓冲区的字节偏移。
在此示例中，多次包含同一标头而结果不同。另外，不必内联读取/写入功能，这只是一个示例。
这是标题：
/* note there's NO include guard in the header file */
#ifndef H__FACIL_IO_MACROS
#define H__FACIL_IO_MACROS
/** Reads an unaligned network ordered byte stream to a 16 bit number. */
#define fio_str2u16(c) \
((uint16_t)(((uint16_t)(((uint8_t *)(c))[0]) << 8) | \
(uint16_t)(((uint8_t *)(c))[1])))
/** Reads an unaligned network ordered byte stream to a 32 bit number. */
#define fio_str2u32(c) \
((uint32_t)(((uint32_t)(((uint8_t *)(c))[0]) << 24) | \
((uint32_t)(((uint8_t *)(c))[1]) << 16) | \
((uint32_t)(((uint8_t *)(c))[2]) << 8) | \
(uint32_t)(((uint8_t *)(c))[3])))
/** Writes a local 16 bit number to an unaligned buffer in network order. */
#define fio_u2str16(buffer, i) \
do { \
((uint8_t *)(buffer))[0] = ((uint16_t)(i) >> 8) & 0xFF; \
((uint8_t *)(buffer))[1] = ((uint16_t)(i)) & 0xFF; \
} while (0);
/** Writes a local 32 bit number to an unaligned buffer in network order. */
#define fio_u2str32(buffer, i) \
do { \
((uint8_t *)(buffer))[0] = ((uint32_t)(i) >> 24) & 0xFF; \
((uint8_t *)(buffer))[1] = ((uint32_t)(i) >> 16) & 0xFF; \
((uint8_t *)(buffer))[2] = ((uint32_t)(i) >> 8) & 0xFF; \
((uint8_t *)(buffer))[3] = ((uint32_t)(i)) & 0xFF; \
} while (0);
/* convert SERIAL_STRUCT_NAME to actual name */
#define SERIAL_STRUCT_MAKE(struct_name) SERIAL_STRUCT_MAKE2(struct_name)
#endif
#if SERIALIZE_TYPE /* create the type */
#undef SERIALIZE_TYPE
#undef SERIAL_STRUCT_FIELD
#define SERIAL_STRUCT_FIELD(name, bits, pos) uint##bits##_t name
#undef SERIAL_STRUCT_MAKE2
#define SERIAL_STRUCT_MAKE2(struct_name) \
typedef struct { \
SERIAL_STRUCT_FIELDS; \
} struct_name##_s;
/* perform macros */
SERIAL_STRUCT_MAKE(SERIAL_STRUCT_NAME)
#elif SERIALIZE_READ /* create reader function */
#undef SERIALIZE_READ
#undef SERIAL_STRUCT_FIELD
#define SERIAL_STRUCT_FIELD(name, bits, pos) \
dest->name = fio_str2u##bits((src + (pos)))
#undef SERIAL_STRUCT_MAKE2
#define SERIAL_STRUCT_MAKE2(struct_name) \
inline static void struct_name_read(struct_name##_s *dest, \
unsigned char *src) { \
SERIAL_STRUCT_FIELDS; \
}
/* perform macros */
SERIAL_STRUCT_MAKE(SERIAL_STRUCT_NAME)
#elif SERIALIZE_WRITE /* create writer function */
#undef SERIALIZE_WRITE
#undef SERIAL_STRUCT_FIELD
#define SERIAL_STRUCT_FIELD(name, bits, pos) \
fio_u2str##bits((dest + (pos)), src->name)
#undef SERIAL_STRUCT_MAKE2
#define SERIAL_STRUCT_MAKE2(struct_name) \
inline static void struct_name##_write(unsigned char *dest, \
struct_name##_s *src) { \
SERIAL_STRUCT_FIELDS; \
}
/* perform macros */
SERIAL_STRUCT_MAKE(SERIAL_STRUCT_NAME)
#endif
在实现文件中，信息可能看起来像这样（同样，可以更改内联方法）：
/* will produce req_file_s as the struct name, but you can change that */
#define SERIAL_STRUCT_NAME req_file
#define SERIAL_STRUCT_FIELDS \
SERIAL_STRUCT_FIELD(start_pos, 32, 0); \
SERIAL_STRUCT_FIELD(byte_count, 32, 4); \
SERIAL_STRUCT_FIELD(name_len, 16, 8)
#define SERIALIZE_TYPE 1
#include "serialize.h"
#define SERIALIZE_READ 1
#include "serialize.h"
#define SERIALIZE_WRITE 1
#include "serialize.h"
可以对此进行调整，因此SERIALIZE_TYPE也声明了这些函数（未定义它们），并且这些函数未内联（因此，仅实现文件对每种类型的标头包含3次。
答案 1 :(得分：1)
xmacros工作。技巧是根据类型使用令牌粘贴和函数别名：
#define htonuint32_t htonl
#define htonuint16_t htons
#define ntohuint32_t ntohl
#define ntohuint16_t ntohl
#define DEF_FIELDS \
DEF_FIELD(uint32_t,start_pos); \
DEF_FIELD(uint32_t,byte_count); \
DEF_FIELD(uint16_t,name_len)
#define DEF_FIELD(t,v) t v
typedef struct __attribute__((__packed__)) req_file {
DEF_FIELDS;
} req_file;
#undef DEF_FIELD
#define DEF_FIELD(t,v) d->v = hton##t(d->v)
void req_file_hton(req_file *d) {
DEF_FIELDS;
}
#undef DEF_FIELD
#define DEF_FIELD(t,v) d->v = ntoh##t(d->v)
void req_file_hton(req_file *d) {
DEF_FIELDS;
}
预处理的代码（经过重新格式化以更清晰地显示）：
typedef struct __attribute__((__packed__)) req_file {
uint32_t start_pos;
uint32_t byte_count;
uint16_t name_len;
} req_file;
void req_file_hton(req_file *d) {
d->start_pos = htonl(d->start_pos);
d->byte_count = htonl(d->byte_count);
d->name_len = htons(d->name_len);
}
void req_file_hton(req_file *d) {
d->start_pos = ntohl(d->start_pos);
d->byte_count = ntohl(d->byte_count);
d->name_len = ntohl(d->name_len);
}
如果具有多个结构，则可以使宏系统复杂化，以便能够生成所有结构和函数。具有2种不同结构的示例：
#define htonuint32_t htonl
#define htonuint16_t htons
#define ntohuint32_t ntohl
#define ntohuint16_t ntohl
#define DEF_FIELDS_req_file \
DEF_FIELD(uint32_t,start_pos); \
DEF_FIELD(uint32_t,byte_count); \
DEF_FIELD(uint16_t,name_len)
#define DEF_FIELDS_other_file \
DEF_FIELD(uint32_t,foo_pos); \
DEF_FIELD(uint32_t,char_count); \
DEF_FIELD(uint16_t,bar_len)
#define STRUCT_DEF(s) \
START_DECL(s) \
DEF_FIELDS_##s; \
END_DECL(s)
#define START_DECL(s) typedef struct __attribute__((__packed__)) s {
#define END_DECL(s) } s
#define DEF_FIELD(t,v) t v
STRUCT_DEF(req_file);
STRUCT_DEF(other_file);
#undef DEF_FIELD
#undef START_DECL
#undef END_DECL
#define DEF_FIELD(t,v) d->v = hton##t(d->v)
#define START_DECL(s) void s##_hton(s *d) {
#define END_DECL(s) }
STRUCT_DEF(req_file);
STRUCT_DEF(other_file);
#undef DEF_FIELD
#undef START_DECL
#define DEF_FIELD(t,v) d->v = ntoh##t(d->v)
#define START_DECL(s) void s##_ntoh(s *d) {
STRUCT_DEF(req_file);
STRUCT_DEF(other_file);
结果：
typedef struct __attribute__((__packed__)) req_file { uint32_t start_pos; uint32_t byte_count; uint16_t name_len; } req_file;
typedef struct __attribute__((__packed__)) other_file { uint32_t foo_pos; uint32_t char_count; uint16_t bar_len; } other_file;
void req_file_hton(req_file *d) { d->start_pos = htonl(d->start_pos); d->byte_count = htonl(d->byte_count); d->name_len = htons(d->name_len); };
void other_file_hton(other_file *d) { d->foo_pos = htonl(d->foo_pos); d->char_count = htonl(d->char_count); d->bar_len = htons(d->bar_len); };
void req_file_ntoh(req_file *d) { d->start_pos = ntohl(d->start_pos); d->byte_count = ntohl(d->byte_count); d->name_len = ntohl(d->name_len); };
void other_file_ntoh(other_file *d) { d->foo_pos = ntohl(d->foo_pos); d->char_count = ntohl(d->char_count); d->bar_len = ntohl(d->bar_len); };
答案 2 :(得分：1)
您可以改编Antony Polukhin的magic_get库，以将任何（任意）结构转换为不同的字节顺序-就像现在可以将任意结构打印到ostream一样。
答案 3 :(得分：1)
好吧，很简单。
#include <stdint.h>
#include <arpa/inet.h>
/* the NETSTRUCT library ------------------------------- */
// for uint32_t
#define NETSTRUCT_dec_uint32_t(n) uint32_t n;
#define NETSTRUCT_hton_uint32_t(n) t->n = htonl(t->n);
#define NETSTRUCT_ntoh_uint32_t(n) t->n = ntohl(t->n);
// for uint16_t
#define NETSTRUCT_dec_uint16_t(n) uint16_t n;
#define NETSTRUCT_hton_uint16_t(n) t->n = htons(t->n);
#define NETSTRUCT_ntoh_uint16_t(n) t->n = ntohs(t->n);
// dec hton ntoh switch
#define NETSTRUCT_dec(type, name) NETSTRUCT_dec_##type(name)
#define NETSTRUCT_hton(type, name) NETSTRUCT_hton_##type(name)
#define NETSTRUCT_ntoh(type, name) NETSTRUCT_ntoh_##type(name)
// calls NETSTRUCT_mod
#define NETSTRUCT1(mod, a) NETSTRUCT_##mod a
#define NETSTRUCT2(mod, a, ...) NETSTRUCT1(mod, a) NETSTRUCT1(mod, __VA_ARGS__)
#define NETSTRUCT3(mod, a, ...) NETSTRUCT1(mod, a) NETSTRUCT2(mod, __VA_ARGS__)
#define NETSTRUCT4(mod, a, ...) NETSTRUCT1(mod, a) NETSTRUCT3(mod, __VA_ARGS__)
// TO DO: all up to NETSTRUCT64
// variadic macro overload
#define NETSTRUCT_GET(_1,_2,_3,_4,NAME,...) NAME
// Overlads VA_ARGS with specified mod
#define NETSTRUCT_IN(mod, ...) \
NETSTRUCT_GET(__VA_ARGS__, NETSTRUCT4, NETSTRUCT3, NETSTRUCT2, NETSTRUCT1) \
(mod, __VA_ARGS__)
// entrypoint of out library
#define NETSTRUCT(name, ...) \
\
struct name { \
NETSTRUCT_IN(dec, __VA_ARGS__) \
} __attribute__((__packed__)); \
\
void name##_hton(struct name *t) { \
NETSTRUCT_IN(hton, __VA_ARGS__) \
} \
\
void name##_ntoh(struct name *t) { \
NETSTRUCT_IN(ntoh, __VA_ARGS__) \
}
/* -------------------------------------------------------- */
// adding custom type
#define NETSTRUCT_dec_uint8_t_arr_8(n) uint8_t n[8];
#define NETSTRUCT_hton_uint8_t_arr_8(n) do{}while(0);
#define NETSTRUCT_ntoh_uint8_t_arr_8(n) do{}while(0);
NETSTRUCT(reg_file,
(uint32_t, start_pos),
(uint32_t, byte_count),
(uint16_t, name_len),
(uint8_t_arr_8, example_custom_array)
);
int main() {
struct reg_file t;
reg_file_hton(&t);
reg_file_ntoh(&t);
}
我已经编写了mactos，因此很容易添加另一个功能，很可能是void name##serialize(char *in)和void name##deserialize(const char *out)。可以对设计进行稍微的重构，以便类型回调NETSTRUCT_dec_*可以使用两个或什至数量未知的ex参数。 NETSTRUCT(name, (type_callback_suffix, (arguments, arguments2)))。
@edit添加了自定义数组类型示例，并更改了某些行的顺序。