c语言中struct小结

1.基本数据类型占用字节（32位的机器）

#include<stdio.h>
#include<stdlib.h>

void BytePossess()
{
    printf(" char : %dByte\n",sizeof(char));
    printf(" signed char : %dByte\n",sizeof(signed char));
    printf(" unsigned char : %dByte\n",sizeof(unsigned char));
    printf(" short int : %dByte\n",sizeof(short int));
    printf(" unsigned short int : %dByte\n",sizeof(unsigned short int));
    printf(" int : %dByte\n",sizeof(int));
    printf(" signed int : %dByte\n",sizeof(signed int));
    printf(" unsigned int : %dByte\n",sizeof(unsigned int));
    printf(" long int : %dByte\n",sizeof(unsigned int));
    printf(" unsigned long int : %dByte\n",sizeof(unsigned long int));
    printf(" double : %dByte\n",sizeof(double));
    printf("  float : %dByte\n",sizeof(float));
}

                char : 1Byte
         signed char : 1Byte
       unsigned char : 1Byte
           short int : 2Byte
  unsigned short int : 2Byte
                 int : 4Byte
          signed int : 4Byte
        unsigned int : 4Byte
            long int : 4Byte
   unsigned long int : 4Byte
              double : 8Byte
               float : 4Byte

2：结构体：涉及内存对齐以提高内存的利用率，位段的使用

typedef struct
{
    char a;
    int b;
    char c;
}Astruct;

struct Bstruct
{
    char a;
    char b;
    int c;
};

struct Cstruct
{
    int x:1;
    int y:14;
    int Z:32;
    int W:1;
//    int z:33;//不可超过int 32的长度
};

int main()
{
    BytePossess();
    printf("----------分割线-------------\n");
    char a=129;
    unsigned char b=-1;
    printf("%d\n",a);
    printf("%d\n",b);
    printf("----------分割线-------------\n");
    Astruct A;//Astruct是typedef定义的新类型，用这新类型定义变量
    struct Bstruct B;
    struct Cstruct C;
    printf("A:%dByte\n",sizeof(A));//32机器的内存是以4字节对齐的，char 4,int 4,char 4   总12
    printf("B:%dByte\n",sizeof(B));//char char 两个占4，int 4  总8//提高了内存的利用率
    printf("C:%dByte\n",sizeof(C));//位段：节省存储空间，还有好几个好处。自己百度，谷歌
    return 0;
}

----------分割线-------------
-127
255
----------分割线-------------
A:12Byte
B:8Byte
C:12Byte