學點 C 語言(29): 資料類型 – 定義新類型(typedef)

自訂的類型名一般要大寫, 以提示這是自命名的類型.
1. 把 unsigned long 更名為 UINT:

#include <stdio.h>int main(void){    typedef unsigned long UINT;    UINT num = 1234567890;    printf("%lu\n", num);        getchar();    return 0;}

2. 給一個結構重新命名:

#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("結構大小: %u, %u, %u", sizeof(struct Rec), sizeof r1, sizeof(MYREC));        getchar();    return 0;}

3. 把整數指標定義為: PINT:

#include <stdio.h>int main(void){    typedef int * PINT;    int num = 123;    PINT p = &num;    printf("%d, %p\d", *p, p);        getchar();    return 0;}

4. 同時用於結構定義:

#include <stdio.h>int main(void){    struct Rec1 {        int x,y;    } r1 = {11, 22};  /* 同時定義了變數 r1 */    typedef struct Rec2 {        double a,b;    } REC3;           /* 此時的 REC3 不是變數, 而是新定義的類型*/    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;}