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C语言中巧妙的使用#和##(实例讲解)(一)
2018-01-12 06:06:49 】 浏览:55
Tags:言中 巧妙 使用 实例 讲解

举个例子来说:

正常的定义一个结构体 的过程是

typdef struct __str__Student  
{
    char* name;
    int id;
}Student;

但是当大量的使用结构体定义的时候会出现定义显得过于麻烦,巧妙的使用 ## 连接符能够很好的解决这个问题如下:

#include <stdio.h>

#define STRUCT(type) typedef struct _tag_##type type;\
struct _tag_##type

STRUCT(Student)   //当一个工程中有大量的结构体的时候,这样使用能够节省大量的时间
{
    char* name;
    int id;
};

int main()
{

    Student s1;
    Student s2;

    s1.name = "s1";
    s1.id = 0;

    s2.name = "s2";
    s2.id = 1;

    printf("%s\n", s1.name);
    printf("%d\n", s1.id);
    printf("%s\n", s2.name);
    printf("%d\n", s2.id);

    return 0;
}

在linux上按照单步编译 gcc -E test.c -0 test.i 结果如下:

test.i输出:

在test.i中前面的都是stdio.h中的文件,不需要看直接看后面的就是上述连接符处理的过程:

# 1 "aa.c"
# 1 "<built-in>"
# 1 "<command-line>"
# 1 "/usr/include/stdc-predef.h" 1 3 4
# 1 "<command-line>" 2
# 1 "aa.c"
# 1 "/usr/include/stdio.h" 1 3 4
# 27 "/usr/include/stdio.h" 3 4
# 1 "/usr/include/features.h" 1 3 4
# 367 "/usr/include/features.h" 3 4
# 1 "/usr/include/x86_64-linux-gnu/sys/cdefs.h" 1 3 4
# 410 "/usr/include/x86_64-linux-gnu/sys/cdefs.h" 3 4
# 1 "/usr/include/x86_64-linux-gnu/bits/wordsize.h" 1 3 4
# 411 "/usr/include/x86_64-linux-gnu/sys/cdefs.h" 2 3 4
# 368 "/usr/include/features.h" 2 3 4
# 391 "/usr/include/features.h" 3 4
# 1 "/usr/include/x86_64-linux-gnu/gnu/stubs.h" 1 3 4
# 10 "/usr/include/x86_64-linux-gnu/gnu/stubs.h" 3 4
# 1 "/usr/include/x86_64-linux-gnu/gnu/stubs-64.h" 1 3 4
# 11 "/usr/include/x86_64-linux-gnu/gnu/stubs.h" 2 3 4
# 392 "/usr/include/features.h" 2 3 4
# 28 "/usr/include/stdio.h" 2 3 4





# 1 "/usr/lib/gcc/x86_64-linux-gnu/5/include/stddef.h" 1 3 4
# 216 "/usr/lib/gcc/x86_64-linux-gnu/5/include/stddef.h" 3 4

# 216 "/usr/lib/gcc/x86_64-linux-gnu/5/include/stddef.h" 3 4
typedef long unsigned int size_t;
# 34 "/usr/include/stdio.h" 2 3 4

# 1 "/usr/include/x86_64-linux-gnu/bits/types.h" 1 3 4
# 27 "/usr/include/x86_64-linux-gnu/bits/types.h" 3 4
# 1 "/usr/include/x86_64-linux-gnu/bits/wordsize.h" 1 3 4
# 28 "/usr/include/x86_64-linux-gnu/bits/types.h" 2 3 4


typedef unsigned char __u_char;
typedef unsigned short int __u_short;
typedef unsigned int __u_int;
typedef unsigned long int __u_long;


typedef signed char __int8_t;
typedef unsigned char __uint8_t;
typedef signed short int __int16_t;
typedef unsigned short int __uint16_t;
typedef signed int __int32_t;
typedef unsigned int __uint32_t;

typedef signed long int __int64_t;
typedef unsigned long int __uint64_t;







typedef long int __quad_t;
typedef unsigned long int __u_quad_t;
# 121 "/usr/include/x86_64-linux-gnu/bits/types.h" 3 4
# 1 "/usr/include/x86_64-linux-gnu/bits/typesizes.h" 1 3 4
# 122 "/usr/include/x86_64-linux-gnu/bits/types.h" 2 3 4


typedef unsigned long int __dev_t;
typedef unsigned int __uid_t;
typedef unsigned int __gid_t;
typedef unsigned long
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