gerty3000 问道：
创建包含与结构体等效的信息的动态结构是可能的，但很困难。 — 如何做到这一点？我想将动态定义的结构体传递给其他C代码（假设编译器和其他设置相同），而不必复制来自编译器的结构体内存布局例程。我不会在进程内经常访问这些结构体的字段（只初始化一次），因此方便的语法并不是问题。
您无法在某种形式上重复内存布局而不进行复制。它可能不需要完全相同，但最好是如此。以下是大致显示如何完成此操作的示例代码。
main()程序。它调用了other_function()，演示了我在数据结构中定义的结构确实完全匹配。该数据假定64位机器上double必须对齐到8字节边界（因此结构中有4字节的空洞）；您需要调整数据以适应double可以在4字节边界上的机器。#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
/* This is the type that will be simulated dynamically */
/*
struct simulated
{
int number;
double value;
char string[32];
};
*/
/* SOF structure.h */
typedef enum Type { INT, DOUBLE, STRING } Type;
typedef struct Descriptor
{
size_t offset;
Type type;
size_t type_size;
size_t array_dim;
char name[32];
} Descriptor;
typedef struct Structure
{
size_t size;
char name[32];
Descriptor *details;
} Structure;
extern void *allocate_structure(const Structure *structure);
extern void deallocate_structure(void *structure);
extern void *pointer_to_element(void *p, const Descriptor *d);
extern int get_int_element(void *p, const Descriptor *d);
extern void set_int_element(void *p, const Descriptor *d, int newval);
extern double get_double_element(void *p, const Descriptor *d);
extern void set_double_element(void *p, const Descriptor *d, double newval);
extern char *get_string_element(void *p, const Descriptor *d);
extern void set_string_element(void *p, const Descriptor *d, char *newval);
/* EOF structure.h */
static Descriptor details[] =
{
{ 0, INT, sizeof(int), 1, "number" },
{ 8, DOUBLE, sizeof(double), 1, "value" },
{ 16, STRING, sizeof(char), 32, "string" },
};
static Structure simulated = { 48, "simulated", details };
void *allocate_structure(const Structure *structure)
{
void *p = calloc(1, structure->size);
return p;
}
void deallocate_structure(void *structure)
{
free(structure);
}
void *pointer_to_element(void *p, const Descriptor *d)
{
void *data = (char *)p + d->offset;
return data;
}
int get_int_element(void *p, const Descriptor *d)
{
assert(d->type == INT);
int *v = pointer_to_element(p, d);
return *v;
}
void set_int_element(void *p, const Descriptor *d, int newval)
{
assert(d->type == INT);
int *v = pointer_to_element(p, d);
*v = newval;
}
double get_double_element(void *p, const Descriptor *d)
{
assert(d->type == DOUBLE);
double *v = pointer_to_element(p, d);
return *v;
}
void set_double_element(void *p, const Descriptor *d, double newval)
{
assert(d->type == DOUBLE);
double *v = pointer_to_element(p, d);
*v = newval;
}
char *get_string_element(void *p, const Descriptor *d)
{
assert(d->type == STRING);
char *v = pointer_to_element(p, d);
return v;
}
void set_string_element(void *p, const Descriptor *d, char *newval)
{
assert(d->type == STRING);
assert(d->array_dim > 1);
size_t len = strlen(newval);
if (len > d->array_dim)
len = d->array_dim - 1;
char *v = pointer_to_element(p, d);
memmove(v, newval, len);
v[len] = '\0';
}
extern void other_function(void *p);
int main(void)
{
void *sp = allocate_structure(&simulated);
if (sp != 0)
{
set_int_element(sp, &simulated.details[0], 37);
set_double_element(sp, &simulated.details[1], 3.14159);
set_string_element(sp, &simulated.details[2], "Absolute nonsense");
printf("Main (before):\n");
printf("Integer: %d\n", get_int_element(sp, &simulated.details[0]));
printf("Double: %f\n", get_double_element(sp, &simulated.details[1]));
printf("String: %s\n", get_string_element(sp, &simulated.details[2]));
other_function(sp);
printf("Main (after):\n");
printf("Integer: %d\n", get_int_element(sp, &simulated.details[0]));
printf("Double: %f\n", get_double_element(sp, &simulated.details[1]));
printf("String: %s\n", get_string_element(sp, &simulated.details[2]));
deallocate_structure(sp);
}
return 0;
}
#include <stdio.h>
#include <string.h>
extern void other_function(void *p);
struct simulated
{
int number;
double value;
char string[32];
};
void other_function(void *p)
{
struct simulated *s = (struct simulated *)p;
printf("Other function:\n");
printf("Integer: %d\n", s->number);
printf("Double: %f\n", s->value);
printf("String: %s\n", s->string);
s->number *= 2;
s->value /= 2;
strcpy(s->string, "Codswallop");
}
Main (before):
Integer: 37
Double: 3.141590
String: Absolute nonsense
Other function:
Integer: 37
Double: 3.141590
String: Absolute nonsense
Main (after):
Integer: 74
Double: 1.570795
String: Codswallop
显然，这段代码还没有准备好投入生产。它足以演示可以做什么。你需要处理的一个问题是正确初始化Structure和Descriptor数据。在这种代码中不能放太多的断言。例如，在get_double_element()中，我应该真正拥有assert(d->size == sizeof(double);。还可以包括assert(d->offset % sizeof(double) == 0);以确保double元素被正确对齐。或者你可能有一个validate_structure(const Structure *sp);函数来执行所有这些验证检查。你需要一个函数void dump_structure(FILE *fp, const char *tag, const Structure *sp);将定义的结构转储到给定的文件中，并在标签之前进行辅助调试。等等。
这段代码是纯C；它无法由C++编译器编译为C++。没有足够的强制转换来满足C++编译器。
uint32_t等类型）。您不使用#pragma pack，它是非标准的。但是您确实需要担心结构中是否有填充以及是否将其发送到网络等问题。通过仔细定义数据的发送方式（因此接收），并设计程序以正确打包/解包，可以避免大部分这些问题。 - Jonathan Leffler对于动态结构，答案是否定的。
如果你知道数据是什么，在C++中，你可以使用重载的<<运算符来从流中读取数据。
在C语言中，你可以将流转换为字符串，假设你知道数据的长度，并使用类似sscanf的函数来读取数据。
你无法定义源代码级别的结构体，但是可以通过设置数据结构来存储要通信的每个字段的名称/标签和偏移量，然后根据它在正确的偏移量处存储/读取数据。确保将所有类型对齐到大小为sizeof(type)的倍数，以实现可移植性。当然，除非您确定客户端和服务器具有相同的数据表示（字节序和其他考虑因素）并且真正需要直接访问的性能，否则我会编写适当的序列化和反序列化例程而不是直接访问。
基于gerty3000的答案，我制作了一个库。我从最终用户那里抽象出了一些东西。虽然很难，但最终还是成功了。如果有任何改进意见，我很乐意听取建议。这是代码。
type-machine.h // 定义类型和函数原型
#ifndef TYPE_MACHINE_H
#define TYPE_MACHINE_H
#ifdef __cplusplus
extern "C" {
#endif
#define B8 char
#define B8U unsigned char
#define B16 short
#define B16U unsigned short
#define B32 int
#define B32U unsigned int
#define B64 long long int
#define B64U unsigned long long int
#define BP32 float
#define BP64 double
#define BIT_ON(var,bit) ((var)=((var) | (bit)))
#define BIT_OFF(var,bit) ((var)=((var) & (~bit)))
#define BIT_IS_ON(var,bit) (var & bit)
#define PAIR(position,value) ((value)=((position) << (1)))
typedef struct Bit8Tag BIT;
typedef enum {
Off, On
} STATUS;
typedef enum {
B8_T, B8U_T, B16_T, B16U_T, B32_T, B64_T, B64U_T, B32U_T, BP32_T, BP64_T
} TYPE;
typedef struct ClassFieldTag ClassField;
typedef struct ClassTag Class;
typedef enum {
CLASS_SIZE, CLASS_INSERT, CLASS_SHOW
} CLASS_MODE;
#if (defined(WIN32) || defined(WINDOWS_XP))
#define is_win()(1)
#else
#define is_win()(0)
#define TYPE_CALL
#define TYPE_TYPE
#endif // WIN32
#include <math.h>
#include <string.h>
#include <assert.h>
#define area(a,b) ((a)*(b))
#define radian(x,y)(atan2(y,x))
#define angle(a)( (a * (180 / M_PI)) + 180)
#if defined WIN32
#define ARIAL_PATH "C:/Windows/Fonts/arial.ttf\0"
#else
#define ARIAL_PATH "home/media/TheGreat/\0"
#endif
struct ClassFieldTag {
TYPE type;
size_t mem, size, len;
B8 name[32];
struct ClassFieldTag * next, *preview;
};
extern ClassField * class_set_push();
extern ClassField * class_field_set(ClassField * set, TYPE type, B8 * name, size_t len, size_t mem);
extern STATUS class_set_next_back(ClassField ** set, ClassField * next);
extern STATUS class_set_next_front(ClassField ** set, ClassField * next);
extern STATUS class_insert_back(Class * set, TYPE type, B8 * name, size_t len);
extern STATUS class_insert_front(Class * set, TYPE type, B8 * name, size_t len);
struct ClassTag {
B8 name[32];
void * data;
B8 * String;
B16 Short;
B16U UShort;
B32 Int;
B32U UInt;
B64 Long;
B64 ULong;
BP32 Float;
BP64 Double;
ClassField * field;
};
Class * class_push(B8 name[32]);
extern STATUS class_zero(Class * set, B8 name[32]);
extern void class_data_push(Class * set);
extern void class_data_pop(Class * set);
extern void * class_set_to(Class * set, ClassField * field);
extern void class_int_set(Class * set, ClassField * field, B32 value);
extern B32 class_int_get(Class * set, ClassField * field);
extern void class_double_set(Class * set, ClassField * field, BP64 value);
extern BP64 class_double_get(Class * set, ClassField * field);
extern void class_string_set(Class * set, ClassField * field, B8 * value);
extern B8 * class_string_get(Class * set, ClassField * field);
extern void class_mode(Class * set, ClassField * field, CLASS_MODE mode);
extern void class_field_pop(Class * set);
extern void class_pop(Class * set);
extern STATUS class_ex(Class * mine);
struct Bit8Tag {
unsigned b16 : 16;
};
extern void bit_on(BIT * value, int bit);
extern void bit_off(BIT * value, int bit);
extern STATUS bit_is_on(BIT value, int bit);
extern B32U strsub(B8 * data, B8 * key);
#ifdef __cplusplus
}
#endif
#endif // TYPE_MACHINE_H
type-machine.c // 声明这些函数
#include <Place/include/type-machine.h>
#include <malloc.h>
#include <stdio.h>
Class * class_push(B8 name[32]) {
Class * set = (Class *) malloc(sizeof (Class));
if(class_zero(set,name)){
return(set);
}
return(NULL);
}
void class_data_push(Class * set) {
B32 class_size = sizeof (Class), class_field_size = sizeof (ClassField);
if (set) {
if (class_size < sizeof (set))class_size = sizeof (set);
if (class_field_size < sizeof (set->field))class_field_size = sizeof (set->field);
}
set->data = malloc(class_size + class_field_size + 1);
}
void class_data_pop(Class * set) {
if (set && set->data) {
free(set->data);
}
}
void * class_set_to(Class * set, ClassField * field) {
if (set && set->data && field) {
void * data = (char *) set->data + field->mem;
return data;
}
return (NULL);
}
void class_int_set(Class * set, ClassField * field, B32 value) {
if (set) {
assert(field->type == B32_T);
B32 * update = class_set_to(set, field);
*update = value;
}
}
B32 class_int_get(Class * set, ClassField * field) {
if (set) {
assert(field->type == B32_T);
B32 * data = class_set_to(set, field);
return (*data);
}
return (0);
}
void class_double_set(Class * set, ClassField * field, BP64 value) {
if (set) {
assert(field->type == BP64_T);
BP64 * update = class_set_to(set, field);
*update = value;
}
}
BP64 class_double_get(Class * set, ClassField * field) {
if (set) {
assert(field->type == BP64_T);
BP64 * data = class_set_to(set, field);
return (*data);
}
return (0);
}
void class_string_set(Class * set, ClassField * field, B8 * value) {
if (set && field && field->len > 1 && value) {
assert(field->type == B8_T);
size_t len = strlen(value);
if (len < 2) {
len = 2;
}
if (len > field->len)len = field->len - 1;
B8 * buffer = class_set_to(set, field);
if (buffer) {
memmove(buffer, value, len);
buffer[len] = '\0';
}
}
}
B8 * class_string_get(Class * set, ClassField * field) {
if (set && field) {
assert(field->type == B8_T);
B8 * data = class_set_to(set, field);
return (data);
}
return (NULL);
}
STATUS class_zero(Class * set, B8 * name) {
if (set) {
set->String = NULL;
set->Short = 0;
set->UShort = 0;
set->Int = 0;
set->UInt = 0;
set->Long = 0;
set->ULong = 0;
set->Float = 0;
set->Double = 0;
set->data = NULL;
memset(set->name, 0, sizeof (set->name));
if (name)memmove(set->name, name, strlen(name));
set->field = NULL;
return (On);
}
return (Off);
}
ClassField * class_set_push() {
return (malloc(sizeof (ClassField)));
}
void class_field_pop(Class * set) {
if (set) {
ClassField * field = set->field;
while (field) {
ClassField * next = field->next;
if (field) {
free(field);
field = NULL;
}
field = next;
}
}
}
void class_pop(Class * set) {
if (set) {
class_data_pop(set);
class_field_pop(set);
free(set);
set = NULL;
}
}
ClassField * class_field_set(ClassField * field, TYPE type, B8 * name, size_t len, size_t mem) {
if (field) {
size_t lenght = (name) ? strlen(name) : 0;
if (lenght > 32) {
lenght = 31;
}
memcpy(field->name, name, lenght);
field->name[lenght] = 0;
field->type = type;
field->mem = mem;
field->len = len;
class_mode(NULL, field, CLASS_SIZE);
field->next = NULL;
field->preview = NULL;
return (field);
}
return (NULL);
}
STATUS class_set_next_back(ClassField ** field, ClassField * next) {
if (next == NULL)return (Off);
next->next = *field;
if (*field != NULL) {
(*field)->preview = next;
}
*field = next;
return (On);
}
STATUS class_set_next_front(ClassField ** field, ClassField * next) {
if (next == NULL)return (Off);
if (*field != NULL) {
ClassField * update = *field, *preview = NULL;
while (update->next != NULL) {
preview = update;
update = update->next;
}
update->preview = preview;
update->next = next;
return (On);
}
*field = next;
return (On);
}
STATUS class_insert_back(Class * set, TYPE type, B8 * name, size_t len) {
if (class_set_next_back(&set->field, class_field_set(class_set_push(), type, name, len, 0))) {
ClassField * preview = set->field;
if (preview->next) {
preview->mem = preview->next->mem + preview->next->size;
}
return (On);
}
return (Off);
}
STATUS class_insert_front(Class * set, TYPE type, B8 * name, size_t len) {
ClassField * next = class_field_set(class_set_push(), type, name, len, 0);
if (class_set_next_front(&set->field, next)) {
ClassField * preview = set->field;
while (preview) {
if (preview->next) {
if (preview->next == next) {
next->mem = preview->mem + preview->size;
}
}
preview = preview->next;
}
return (On);
}
return (Off);
}
void class_mode(Class * set, ClassField * field, CLASS_MODE mode) {
if (field) {
switch (field->type) {
case B8_T:
{
switch (mode) {
case CLASS_SHOW:
{
printf("%s: %s\n", field->name, class_string_get(set, field));
}
break;
case CLASS_SIZE:
{
field->size = field->len * sizeof (B8);
}
break;
case CLASS_INSERT:
{
class_string_set(set, field, set->String);
}
break;
}
}
break;
case B8U_T:
{
switch (mode) {
case CLASS_SHOW:
{
printf("%s: %s\n", field->name, class_string_get(set, field));
}
break;
case CLASS_SIZE:
{
field->size = field->len * sizeof (B8U);
}
break;
case CLASS_INSERT:
{
class_string_set(set, field, set->String);
}
break;
}
}
break;
case B16_T:
{
switch (mode) {
case CLASS_SHOW:
{
printf("%s: [%i]\n", field->name, class_int_get(set, field));
}
break;
case CLASS_SIZE:
{
field->size = sizeof (B16);
}
break;
case CLASS_INSERT:
{
class_int_set(set, field, set->Int);
}
break;
}
}
break;
case B16U_T:
{
switch (mode) {
case CLASS_SHOW:
{
printf("%s: [%i]\n", field->name, class_int_get(set, field));
}
break;
case CLASS_SIZE:
{
field->size = sizeof (B16U);
}
break;
case CLASS_INSERT:
{
class_int_set(set, field, set->Int);
}
break;
}
}
break;
case B32_T:
{
switch (mode) {
case CLASS_SHOW:
{
printf("%s: %i\n", field->name, class_int_get(set, field));
}
break;
case CLASS_SIZE:
{
field->size = sizeof (B32);
}
break;
case CLASS_INSERT:
{
class_int_set(set, field, set->Int);
}
break;
}
}
break;
case B32U_T:
{
switch (mode) {
case CLASS_SHOW:
{
printf("%s: [%i]\n", field->name, class_int_get(set, field));
}
break;
case CLASS_SIZE:
{
field->size = sizeof (B32U);
}
break;
case CLASS_INSERT:
{
class_int_set(set, field, set->Int);
}
break;
}
}
break;
case B64_T:
{
switch (mode) {
case CLASS_SHOW:
{
printf("%s: [%i]\n", field->name, class_int_get(set, field));
}
break;
case CLASS_SIZE:
{
field->size = sizeof (B64);
}
break;
case CLASS_INSERT:
{
class_int_set(set, field, set->Int);
}
break;
}
}
break;
case B64U_T:
{
switch (mode) {
case CLASS_SHOW:
{
printf("%s: [%i]\n", field->name, class_int_get(set, field));
}
break;
case CLASS_SIZE:
{
field->size = sizeof (B64U);
}
break;
case CLASS_INSERT:
{
class_int_set(set, field, set->Int);
}
break;
}
}
break;
case BP32_T:
{
switch (mode) {
case CLASS_SHOW:
{
printf("%s: [%lf]\n", field->name, class_double_get(set, field));
}
break;
case CLASS_SIZE:
{
field->size = sizeof (BP32);
}
break;
case CLASS_INSERT:
{
class_double_set(set, field, set->Double);
}
break;
}
}
break;
case BP64_T:
{
switch (mode) {
case CLASS_SHOW:
{
printf("%s: [%lf]\n", field->name, class_double_get(set, field));
}
break;
case CLASS_SIZE:
{
field->size = sizeof (BP64);
}
break;
case CLASS_INSERT:
{
class_double_set(set, field, set->Double);
}
break;
}
}
break;
}
}
}
void bit_on(BIT * value, int bit) {
BIT_ON(value->b16, bit);
}
void bit_off(BIT * value, int bit) {
BIT_OFF(value->b16, bit);
}
STATUS bit_is_on(BIT value, int bit) {
if (value.b16 & bit)return (On);
return (Off);
}
B32U strsub(B8 * data, B8 * key) {
if (data && key) {
B8 *d = data;
B32U len = strlen(key), p = 0;
if (len > strlen(d))return (0);
while (*d != '\0') {
if (*(d + len) != '\0') {
B32U x = 0;
while (x <= len) {
if (key[x] == *d) {
*d++;
p++;
} else break;
x++;
}
if (x == len)return (p);
} else if (len == 1) {
if (*d == key[0])return (p);
}
p++;
*d++;
}
}
return (0);
}
main.c // 测试中....
#include "network.h"
#include <conio.h>
STATUS class_ex(Class * set) {
class_data_push(set);
if (set->data) {
ClassField * field = set->field;
while (field) {
if (!strcmp(field->name, "peso")) {
set->Double = 65.5;
}
if (!strcmp(field->name, "idade")) {
set->Int = 29;
}
if (!strcmp(field->name, "nome")) {
set->String = "Lisias de Castro Martins";
}
if (!strcmp(field->name, "endereco")) {
set->String = "Rua Mae D'Agua";
}
class_mode(set, field, CLASS_INSERT);
class_mode(set, field, CLASS_SHOW);
field = field->next;
}
return (On);
}
return (Off);
}
int main(int argc, char** argv) {
STATUS client_start = On;
if (client_start) {
Class * client = class_push("Client");;
class_insert_back(client, BP64_T, "peso", 1);
class_insert_back(client, B8_T, "endereco", 32);
class_insert_back(client, B32_T, "idade", 1);
class_insert_back(client, B8_T, "nome", 64);
printf("Classe[%s]\n\n", client->name);
if (class_ex(client)) {
}
class_pop(client);
getch();
}
return (EXIT_SUCCESS);
}
我还需要实现short double和其他一些函数，但它正在工作中。