学点 C 语言(29): 数据类型 定义新类型(typedef)

自定义的类型名一般要大写, 以提示这是自命名的类型.

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1. 把 unsigned long 更名为 UINT:

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#include <stdio.h>

int main(void)
{
    typedef unsigned long UINT;

    UINT num = 1234567890;
    printf("%lu\n", num);
    
    getchar();
    return 0;
}

2. 给一个结构重命名:

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#include <stdio.h>

int main(void)
{
    struct Rec {
        char c;
        int  i;
        long d;
    };

    typedef struct Rec MYREC;

    MYREC r1;

    r1.c = 1;
    r1.i = 2;
    r1.d = 3;
    
    printf("%d, %d, %d\n", r1.c, r1.i, r1.d);
    printf("结构大小: %u, %u, %u", sizeof(struct Rec), sizeof r1, sizeof(MYREC));
    
    getchar();
    return 0;
}

3. 把整数指针定义为: PINT:

---

#include <stdio.h>

int main(void)
{
    typedef int * PINT;

    int num = 123;
    PINT p = #

    printf("%d, %p\d", *p, p);
    
    getchar();
    return 0;
}

4. 同时用于结构定义:

---

#include <stdio.h>

int main(void)
{
    struct Rec1 {
        int x,y;
    } r1 = {11, 22};  /* 同时定义了变量 r1 */

    typedef struct Rec2 {
        double a,b;
    } REC3;           /* 此时的 REC3 不是变量, 而是新定义的类型*/

    REC3 r2 = {1.1, 2.2};
    
    printf("%d, %d\n", sizeof(struct Rec1), sizeof(struct Rec2));
    printf("%d, %d, %d\n", sizeof(REC3), sizeof r1, sizeof r2);

    printf("\n%d, %d", r1.x, r1.y);
    printf("\n%g, %g", r2.a, r2.b);
    
    getchar();
    return 0;
}