C语言各数据类型的内存映像

#include <stdio.h>int main(){    signed int smin = 1<<31;    signed int smax = (1<<31)-1;    printf("%d\n",smin);    // -2147483648

    printf("%d\n",smax);    // 2147483647

    unsigned int umax = -1;    printf("%u\n",umax);    // 4294967295

    umax = (1<<32)-1;    printf("%u\n",umax);    // 4294967295}

    unsigned int a=4294967290;    int b=-6; 

    printf("%d\n",a==b); // 1 , b promotes to unsigned

#include <stdio.h>void printByte(double d){    int bs = sizeof d;    unsigned char *ch = (unsigned char*)&d;    for(int i=0;i<bs;i++)        printf("%.2X ",*(ch+i));

}int main(){    int n = 0x01020304;    if(*(char*)&n == 4)        printf("小端：");//小端：

    double d = 15.75; // 1111.11, 指数位值：1023+3

    //0 100 0000 0010 1111100000000000000000000000000000000000000000000000

    printByte(d);//00 00 00 00 00 80 2F 40

    // 40              2F               80

    // 0100 0000 0010 1111 1000 0000

    getchar();

}

#include <stdio.h>typedef struct packed_double {

    unsigned int low32;    // 小数位 低32位

    unsigned int low20:20; // 小数位 低33-52位

    unsigned int exp11:11; // 指数位 低53-63位，移码1023+二进制整数位-1

    unsigned int sign:1;  // 符号位} packed_double;typedef union {    double d;

    packed_double b;

} packed;int main(){

    packed pd;

    pd.d = -15.75;

    pd.d = 12.3;    printf("%u %u %u %u\n",pd.b.sign,pd.b.exp11,pd.b.low20,pd.b.low32);

    getchar(); 

    return 0;

}/*

0 1026 1015808 0

*/

#include <stdio.h>void printArr(short arr[],int len){    for(int i=0;i<len;i++)

    {        printf("%d ",*(arr+i));

    }    printf("\n");

}int main(){

    short arr[] = {1,3,2};    int len = sizeof arr / sizeof *arr;

    printArr(arr,len);

}

#include <stdio.h>int main(){    enum Nm{LOSS,TIE,WIN}nm; // 实质是一个整型，成员只是可能的右值（符号常量）的枚举

    nm = LOSS;    printf("%d ",nm); // 0

    nm = TIE;    printf("%d ",nm); // 1

    nm = WIN;    printf("%d ",nm); // 2

    nm = (enum Nm)3;  

    printf("%d ",nm); // 3

    printf("\n%d",sizeof(enum Nm)); // 4

    getchar();

}

#include <stdio.h>int main(){    union Nn{int a; double b;}nn;// 成员的起始地址相同，值相互覆盖

    nn.a = 123; // 

    printf("起始地址：%X，内存空间占用：%d\n",&nn.a,sizeof nn.a);

    nn.b = 12.3;    printf("起始地址：%X，内存空间占用：%d\n",&nn.a,sizeof nn.b);

    nn.a = 12;    printf("起始地址：%X，内存空间占用：%d\n",&nn.a,sizeof nn.a);

    getchar();

}/*

起始地址：12FF40，内存空间占用：4

起始地址：12FF40，内存空间占用：8

起始地址：12FF40，内存空间占用：4

*/

#include <stdio.h>#include <string.h>#define MAXPARTS 12struct Parts{ // 零件

        int cost;        char supplier[12];        char unit[12] ;

};struct Assembly{ // 装配件

        int n_parts;        struct {

                char partno[12];

                short quan;

        }parts[MAXPARTS];

};struct Inventory{ // 存货类型，或是零件，或是装配件

        char partno[10];        int quan;        enum{PART,ASSEMBLY}type; // 存货类型

        union {                struct Parts parts;

                struct Assembly assembly;

        }info;

};int main(){        struct Inventory screen;

        strcpy(screen.partno,"p001");

        screen.quan = 12;

        screen.type = Inventory::PART;

        screen.info.parts.cost = 122;        strcpy(screen.info.parts.supplier,"hw");        strcpy(screen.info.parts.unit,"pcs");        

        struct Inventory shell;

        strcpy(shell.partno,"a001");

        shell.quan = 4;

        shell.type = Inventory::ASSEMBLY;

        shell.info.assembly.n_parts=22;        strcpy(shell.info.assembly.parts[0].partno,"d001");

        shell.info.assembly.parts[1].quan = 5;        int costs;        if(shell.type == Inventory::ASSEMBLY)

                costs = shell.info.assembly.n_parts;        

        printf("%d\n",costs); //22

        getchar();        return 0;

}

#include <stdio.h>int main()

{    struct demo{char a; short b;int c;} abc; // 成员相对于基址偏移，字节对齐

    abc.b=12;    short *p = (short*)((int)&abc+sizeof(short)); // 模拟编译器计算第2个成员的偏移地址

    printf("%d %d\n",abc.b,*p); // 12 12

    printf("%d\n",sizeof(struct demo));// 8

    getchar();

}

#include <stdio.h>void printBinM(unsigned int n){    for(int i=31;i>=0;i--)        printf("%d",(n & 1<<i)>>i);    printf("\n");

}struct Bf{    

    unsigned a:3;    

    unsigned b:4;    

    unsigned c:5;

}bf;int main(){

    bf.a =1;

    bf.b=15;

    bf.c=3;    int *p = (int*)&bf; // 505

    printf("%d\n",*p);

    printBinM(*p);//00000000000000000000000111111001

    getchar();

}

#include <stdio.h>void printBinM(unsigned int n){    for(int i=31;i>=0;i--)        printf("%d",(n & 1<<i)>>i);    printf("\n");

}int main(){    struct Bf{    

        unsigned a:3;    

        unsigned b:4;    

        unsigned c:5;

    }bf;

    bf.a =1;

    bf.b=15;

    bf.c=3;    int *p = (int*)&bf; // -858996231

    printf("%d\n",*p);

    printBinM(*p);//11001100110011001100000111111001

    getchar();

}