C语言深入了解自定义数据类型的使用

#include <stdio.h>
typedef  unsigned char  byte;
void func()
{
    typedef  byte  uint8;
    uint8 var = 200;
    byte  b   = var;   // 本质为相同类型变量之间的初始化
    printf("sizeof(uint8) = %d\n", sizeof(uint8));
    printf("var = %d\n", var);
    printf("b = %d\n", b);
}
int main()
{
    // uint8 var = 1;   // ERROR
    byte b = 128;
    func();
    printf("sizeof(byte) = %d\n", sizeof(byte));
    printf("b = %d\n", b);
    return 0;
}

#include <stdio.h>
typedef  float(FArr5)[5];        // 定义数组类型名
typedef  int(IFuncII)(int, int); // 定义函数类型名
typedef  FArr5*    PFArr5;
typedef  IFuncII*  PIFuncII;
float g_arr[5] = {0.1, 0.2, 0.3};
int add(int a, int b)
{
    return a + b;
}
int main()
{
    FArr5* pa = &g_arr;  // float(*)[5]
    IFuncII* pf = add;   // int(*)(int,int)
    PFArr5   npa = pa;
    PIFuncII npf = pf;
    int i = 0;
    for(i=0; i<5; i++)
    {
        printf("%f\n", (*pa)[i]);
        printf("%f\n", (*npa)[i]);
    }
    printf("%d\n", pf(2, 3));
    printf("%d\n", npf(2, 3));
    return 0;
}

#include <stdio.h>
#include <string.h>
struct Student
{
    char name[20];
    int id;
    short major;
};
int main()
{
    struct Student s1 = {"Autumn", 908, 1};
    struct Student s2 = s1;
    printf("s1.name = %s\n", s1.name);
    printf("s1.id = %d\n", s1.id);
    printf("s1.major = %d\n", s1.major);
    strcpy(s2.name, "Hu");
    s2.id = 909;
    s2.major = 2;
    printf("s2.name = %s\n", s2.name);
    printf("s2.id = %d\n", s2.id);
    printf("s2.major = %d\n", s2.major);
    return 0;
}

#include <stdio.h>
#include <string.h>
typedef  struct Student  Stu;
struct Student
{
    char name[20];
    int id;
    short major;
};
int main()
{
    Stu s;
    Stu* ps = &s;
    strcpy(ps->name, "Autumn");
    ps->id = 1;
    ps->major = 908;
    (*ps).major = 910;   // ==> s.major = 910
    printf("s.name = %s\n", s.name);
    printf("s.id = %d\n", s.id);
    printf("s.major = %d\n", s.major);
    return 0;
}

#include <stdio.h>
#include <string.h>
struct Test;
struct Test* g_pt;    // 只要有了类型声明就可以创建对应的指针变量
// 必须先给出类型的完整定义才能创建相应类型的变量
struct Test
{
    int a;
    int b;
};
int main()
{
    struct Test t;
    t.a = 1;
    t.b = 2;
    g_pt = &t;
    printf("g_pt = %p\n", g_pt);
    printf("g_pt->a = %d\n", g_pt->a);
    printf("g_pt->b = %d\n", g_pt->b);
    return 0;
}

#include <stdio.h>
#include <string.h>
int main()
{
    struct { int a, b; } v1;
    struct { int a, b; } v2;
    struct { int a, b; }*pv;
    v1.a = 1;
    v1.b = 2;
    v2 = v1;
    pv = &v2;
    return 0;
}

#include <stdio.h>
struct BW
{
    unsigned char a : 4;
    unsigned char b : 2;
    unsigned char c : 2;
};
int main()
{
    struct BW bw = {0};
    bw.a = 10;
    bw.b = 4;   // 4 大于 b 能表示的最大值，因此赋值后 b 回转到 0
    bw.c = 3;
    printf("sizeof(struct BW) = %d\n", sizeof(struct BW));
    printf("bw.a = %d\n", bw.a);
    printf("bw.b = %d\n", bw.b);
    printf("bw.c = %d\n", bw.c);
    return 0;
}

#include <stdio.h>
#include <string.h>
struct Bits1
{
    int a   : 16;
    short b : 8;
    char c  : 8;
    float f;     // float f : 32;   ==> 浮点型成员不能指点位宽度
};
struct Bits2
{
    unsigned char a : 6;
    unsigned char b : 6;
    unsigned char c : 6;
    // unsigned char d : 9;    ==> 指定的位宽度不能大于声明类型的位宽度
};
struct Bits3
{
    unsigned char a : 4;
    unsigned char   : 0;  // 重启一个存储单元表示新的成员
    unsigned char b : 4;
};
int main()
{
    printf("sizeof(Bits1) = %d\n", sizeof(struct Bits1));
    printf("sizeof(Bits2) = %d\n", sizeof(struct Bits2));
    printf("sizeof(Bits3) = %d\n", sizeof(struct Bits3));
    return 0;
}

#include <stdio.h>
#include <string.h>
union UTest
{
    int a;
    float f;
};
struct STest
{
    int a;
    float f;
};
int main()
{
    union UTest ut = {987654321};
    struct STest st = {987654321, 0.1f};
    printf("union UTest size = %d\n", sizeof(union UTest));
    printf("&ut.a = %p\n", &ut.a);
    printf("&ut.f = %p\n", &ut.f);
    printf("struct STest size = %d\n", sizeof(struct STest));
    printf("&st.a = %p\n", &st.a);
    printf("&st.f = %p\n", &st.f);
    printf("ut.a = %d\n", ut.a);
    printf("ut.f = %f\n", ut.f);
    ut.f = 987654321.0f;
    printf("ut.a = %d\n", ut.a);
    printf("ut.f = %f\n", ut.f);
    return 0;
}

#include <stdio.h>
int isLittleEndian()
{
    union
    {
        int i;
        char a[4];
    } test = {0};
    test.i = 1;
    return (test.a[0] == 1);
}
int main()
{
    printf("System Endian: %d\n", isLittleEndian());
    return 0;
}

#include <stdio.h>
#include <string.h>
enum Day { MON = 1, TUE, WED, THU, FRI, SAT, SUN };
enum Season { Spring, Summer = 3, Autumn, Winter = -1 };
enum { CONSTANT = 12345 };
int main()
{
    enum Day d = TUE;
    enum Season s = Winter;
    int i = SUN;
    int j = Autumn;
    printf("d = %d\n", d);   // 2
    printf("s = %d\n", s);   // -1
    printf("i = %d\n", i);   // 7
    printf("j = %d\n", j);   // 4
    d = 0;
    s = -2;
    printf("d = %d\n", d);
    printf("s = %d\n", s);
    printf("sizeof(enum Day) = %d\n", sizeof(enum Day));
    printf("sizeof(enum Season) = %d\n", sizeof(enum Season));
    printf("CONSTANT = %d\n", CONSTANT);
    // CONSTANT = 54321;
    return 0;
}