学点 C 语言(15): 数据类型 sizeof(检测类型大小)

获取类型大小的变量最好不是 int 类型, 而是 size_t 类型;

size_t 在 stdio.h、stddef.h 都有定义.

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1. 获取已知类型的大小:

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#include <stdio.h>
#include <stddef.h>

int main(void)
{
    char n = 2;
    size_t size;

    size = sizeof(char);
    printf("%*u: char\n", n,size);

    size = sizeof(unsigned char);
    printf("%*u: unsigned char\n", n,size);

    size = sizeof(short);
    printf("%*u: short\n", n,size);

    size = sizeof(unsigned short);
    printf("%*u: unsigned short\n", n,size);

    size = sizeof(int);
    printf("%*u: int\n", n,size);

    size = sizeof(unsigned);
    printf("%*u: unsigned\n", n,size);

    size = sizeof(long);
    printf("%*u: long\n", n,size);

    size = sizeof(unsigned long);
    printf("%*u: unsigned long\n", n,size);

    size = sizeof(long long);
    printf("%*u: long long\n", n,size);

    size = sizeof(unsigned long long);
    printf("%*u: unsigned long long\n", n,size);

    size = sizeof(float);
    printf("%*u: float\n", n,size);

    size = sizeof(double);
    printf("%*u: double\n", n,size);

    size = sizeof(long double);
    printf("%*u: long double\n", n,size);

    size = sizeof(wchar_t);
    printf("%*u: wchar_t\n", n,size);
    
    getchar();
    return 0;
}

2. 获取类型大小可根据类型名, 也可根据变量名:

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#include <stdio.h>

int main(void)
{
    int i;
    double d;

    printf("%u, %u\n", sizeof(i), sizeof(int));
    printf("%u, %u\n", sizeof(d), sizeof(double));
    
    getchar();
    return 0;
}

3. 对变量名(非类型名), sizeof 也可以不要括号:

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#include <stdio.h>

int main(void)
{
    int i;
    double d;

    printf("%u\n", sizeof i);
    printf("%u\n", sizeof d);
    
    getchar();
    return 0;
}

4. sizeof(数组变量) 获取的是数组大小(而非维数), 这和 Delphi 很不一样:

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#include <stdio.h>

int main(void)
{
    int nums[10];
    
    printf("%u\n", sizeof nums);                /* 数组大小 */
    printf("%u\n", sizeof(nums) / sizeof(int)); /* 数组维数 */
        
    getchar();
    return 0;
}