我想知道是否可以迭代传递给C99中的变量宏的参数,或者使用任何GCC扩展?
例如,是否可以编写一个泛型宏,将结构及其字段作为参数传递,并打印结构中每个字段的偏移量?
就像这样:
struct a {
int a;
int b;
int c;
};
/* PRN_STRUCT_OFFSETS will print offset of each of the fields
within structure passed as the first argument.
*/
int main(int argc, char *argv[])
{
PRN_STRUCT_OFFSETS(struct a, a, b, c);
return 0;
}
发布于 2018-05-07 12:23:00
无论如何,为了清晰起见,下面的示例代码最多可处理8个字段。如果需要更多的话,只需通过复制来扩展代码(这是因为预处理器不具有递归特性,因为它只读取文件一次。
#include <stdio.h>
#include <stddef.h>
struct a
{
int a;
int b;
int c;
};
struct b
{
int a;
int b;
int c;
int d;
};
#define STRINGIZE(arg) STRINGIZE1(arg)
#define STRINGIZE1(arg) STRINGIZE2(arg)
#define STRINGIZE2(arg) #arg
#define CONCATENATE(arg1, arg2) CONCATENATE1(arg1, arg2)
#define CONCATENATE1(arg1, arg2) CONCATENATE2(arg1, arg2)
#define CONCATENATE2(arg1, arg2) arg1##arg2
/* PRN_STRUCT_OFFSETS will print offset of each of the fields
within structure passed as the first argument.
*/
#define PRN_STRUCT_OFFSETS_1(structure, field, ...) printf(STRINGIZE(structure)":"STRINGIZE(field)"-%d\n", offsetof(structure, field));
#define PRN_STRUCT_OFFSETS_2(structure, field, ...)\
printf(STRINGIZE(structure)":"STRINGIZE(field)"-%d\n", offsetof(structure, field));\
PRN_STRUCT_OFFSETS_1(structure, __VA_ARGS__)
#define PRN_STRUCT_OFFSETS_3(structure, field, ...)\
printf(STRINGIZE(structure)":"STRINGIZE(field)"-%d\n", offsetof(structure, field));\
PRN_STRUCT_OFFSETS_2(structure, __VA_ARGS__)
#define PRN_STRUCT_OFFSETS_4(structure, field, ...)\
printf(STRINGIZE(structure)":"STRINGIZE(field)"-%d\n", offsetof(structure, field));\
PRN_STRUCT_OFFSETS_3(structure, __VA_ARGS__)
#define PRN_STRUCT_OFFSETS_5(structure, field, ...)\
printf(STRINGIZE(structure)":"STRINGIZE(field)"-%d\n", offsetof(structure, field));\
PRN_STRUCT_OFFSETS_4(structure, __VA_ARGS__)
#define PRN_STRUCT_OFFSETS_6(structure, field, ...)\
printf(STRINGIZE(structure)":"STRINGIZE(field)"-%d\n", offsetof(structure, field));\
PRN_STRUCT_OFFSETS_5(structure, __VA_ARGS__)
#define PRN_STRUCT_OFFSETS_7(structure, field, ...)\
printf(STRINGIZE(structure)":"STRINGIZE(field)"-%d\n", offsetof(structure, field));\
PRN_STRUCT_OFFSETS_6(structure, __VA_ARGS__)
#define PRN_STRUCT_OFFSETS_8(structure, field, ...)\
printf(STRINGIZE(structure)":"STRINGIZE(field)"-%d\n", offsetof(structure, field));\
PRN_STRUCT_OFFSETS_7(structure, __VA_ARGS__)
#define PRN_STRUCT_OFFSETS_NARG(...) PRN_STRUCT_OFFSETS_NARG_(__VA_ARGS__, PRN_STRUCT_OFFSETS_RSEQ_N())
#define PRN_STRUCT_OFFSETS_NARG_(...) PRN_STRUCT_OFFSETS_ARG_N(__VA_ARGS__)
#define PRN_STRUCT_OFFSETS_ARG_N(_1, _2, _3, _4, _5, _6, _7, _8, N, ...) N
#define PRN_STRUCT_OFFSETS_RSEQ_N() 8, 7, 6, 5, 4, 3, 2, 1, 0
#define PRN_STRUCT_OFFSETS_(N, structure, field, ...) CONCATENATE(PRN_STRUCT_OFFSETS_, N)(structure, field, __VA_ARGS__)
#define PRN_STRUCT_OFFSETS(structure, field, ...) PRN_STRUCT_OFFSETS_(PRN_STRUCT_OFFSETS_NARG(field, __VA_ARGS__), structure, field, __VA_ARGS__)
int main(int argc, char *argv[])
{
PRN_STRUCT_OFFSETS(struct a, a, b, c);
printf("\n");
PRN_STRUCT_OFFSETS(struct b, a, b, c, d);
return 0;
}
打印出来:
struct a:a-0
struct a:b-4
struct a:c-8
struct b:a-0
struct b:b-4
struct b:c-8
struct b:d-12
编辑:这里有一个稍微不同的版本,试图变得更通用。FOR_EACH(what, ...)
宏应用what
到变量参数列表中的所有其他参数。
因此,只需定义一个宏,该宏接受以下单个参数:
#define DO_STUFF(x) foo(x)
它将应用于列表中的每个参数。因此,对于典型的例子,需要稍微黑一些,但仍然很简洁:
#define PRN_STRUCT_OFFSETS_(structure, field) printf(STRINGIZE(structure)":"STRINGIZE(field)" - offset = %d\n", offsetof(structure, field));
#define PRN_STRUCT_OFFSETS(field) PRN_STRUCT_OFFSETS_(struct a, field)
你就这样运用它:
FOR_EACH(PRN_STRUCT_OFFSETS, a, b, c);
最后,一个完整的示例程序:
#include <stdio.h>
#include <stddef.h>
struct a
{
int a;
int b;
int c;
};
#define STRINGIZE(arg) STRINGIZE1(arg)
#define STRINGIZE1(arg) STRINGIZE2(arg)
#define STRINGIZE2(arg) #arg
#define CONCATENATE(arg1, arg2) CONCATENATE1(arg1, arg2)
#define CONCATENATE1(arg1, arg2) CONCATENATE2(arg1, arg2)
#define CONCATENATE2(arg1, arg2) arg1##arg2
#define FOR_EACH_1(what, x, ...) what(x)
#define FOR_EACH_2(what, x, ...)\
what(x);\
FOR_EACH_1(what, __VA_ARGS__);
#define FOR_EACH_3(what, x, ...)\
what(x);\
FOR_EACH_2(what, __VA_ARGS__);
#define FOR_EACH_4(what, x, ...)\
what(x);\
FOR_EACH_3(what, __VA_ARGS__);
#define FOR_EACH_5(what, x, ...)\
what(x);\
FOR_EACH_4(what, __VA_ARGS__);
#define FOR_EACH_6(what, x, ...)\
what(x);\
FOR_EACH_5(what, __VA_ARGS__);
#define FOR_EACH_7(what, x, ...)\
what(x);\
FOR_EACH_6(what, __VA_ARGS__);
#define FOR_EACH_8(what, x, ...)\
what(x);\
FOR_EACH_7(what, __VA_ARGS__);
#define FOR_EACH_NARG(...) FOR_EACH_NARG_(__VA_ARGS__, FOR_EACH_RSEQ_N())
#define FOR_EACH_NARG_(...) FOR_EACH_ARG_N(__VA_ARGS__)
#define FOR_EACH_ARG_N(_1, _2, _3, _4, _5, _6, _7, _8, N, ...) N
#define FOR_EACH_RSEQ_N() 8, 7, 6, 5, 4, 3, 2, 1, 0
#define FOR_EACH_(N, what, x, ...) CONCATENATE(FOR_EACH_, N)(what, x, __VA_ARGS__)
#define FOR_EACH(what, x, ...) FOR_EACH_(FOR_EACH_NARG(x, __VA_ARGS__), what, x, __VA_ARGS__)
#define PRN_STRUCT_OFFSETS_(structure, field) printf(STRINGIZE(structure)":"STRINGIZE(field)" - offset = %d\n", offsetof(structure, field));
#define PRN_STRUCT_OFFSETS(field) PRN_STRUCT_OFFSETS_(struct a, field)
int main(int argc, char *argv[])
{
FOR_EACH(PRN_STRUCT_OFFSETS, a, b, c);
printf("\n");
return 0;
}
发布于 2018-05-07 13:18:44
foo.h:
// Make a FOREACH macro
#define FE_1(WHAT, X) WHAT(X)
#define FE_2(WHAT, X, ...) WHAT(X)FE_1(WHAT, __VA_ARGS__)
#define FE_3(WHAT, X, ...) WHAT(X)FE_2(WHAT, __VA_ARGS__)
#define FE_4(WHAT, X, ...) WHAT(X)FE_3(WHAT, __VA_ARGS__)
#define FE_5(WHAT, X, ...) WHAT(X)FE_4(WHAT, __VA_ARGS__)
//... repeat as needed
#define GET_MACRO(_1,_2,_3,_4,_5,NAME,...) NAME
#define FOR_EACH(action,...) \
GET_MACRO(__VA_ARGS__,FE_5,FE_4,FE_3,FE_2,FE_1)(action,__VA_ARGS__)
// Example
// Some actions
#define QUALIFIER(X) X::
#define OPEN_NS(X) namespace X {
#define CLOSE_NS(X) }
// Helper function
#define QUALIFIED(NAME,...) FOR_EACH(QUALIFIER,__VA_ARGS__)NAME
// Emit some code
QUALIFIED(MyFoo,Outer,Next,Inner) foo();
FOR_EACH(OPEN_NS,Outer,Next,Inner)
class Foo;
FOR_EACH(CLOSE_NS,Outer,Next,Inner)
CPP foo.h生成:
Outer::Next::Inner::MyFoo foo();
namespace Outer {namespace Next {namespace Inner {
class Foo;
}}}
https://stackoverflow.com/questions/-100008381
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