为什么短期存储为4个字节在C结构？ [英] Why short is stored as 4 bytes in a struct in C?

问题描述

我有以下两个结构：

问题值是sizeof（内容）返回160.结构由11个短裤，6个整数，76个字符，7辆彩车，1双，共增加了158个字节。我已经算三次，还有2字节的区别。

The problem is the sizeof(Content) returns 160. The struct consists of 11 shorts, 6 ints, 76 chars, 7 floats, 1 double, totally adding to 158 bytes. I have counted three times and there is still a 2 byte difference.

typedef struct TIME_T { 
    short year,mon,day; 
    short hour,min,sec; 
} TIME;

typedef struct { 
    int no; 
    char name[20]; 
    char Code[10]; 
    char DASType[10]; 
    short wlen; 
    float VLtd; 
    int samp; 
    int comp; 
    int locationID; 
    short TranMode; 
    char TranIns[12]; 
    short TimerMode; 
    char ClkType[12]; 
    float ClkErr; 
    float lat; 
    float lon; 
    float alt; 
    float azimuth,incident; 
    short weight; 
    short veloc; 
    int oritype; 
    char seismometer[12]; 
    double sens; 
    TIME start_time; 
    int record_samples; 
} Content;

我写了一小块code的打印在结构中每个变量的位置，突然我发现浮法WLEN 需要4个字节。我的code是如下：

I write a small piece of code to print the position of each variables in the struct, and suddenly I find the float wlen takes 4 bytes. My code is as follows:

int main(void)
{   
    Content content;
    printf("Sizeof Content: %d\n", sizeof(content));
    printf("Sizeof int content.no: %d\n", (int)&content.name - (int)&content.no);
    printf("Sizeof char[20] content.name: %d\n", (int)&content.Code - (int)&content.name);
    printf("Sizeof char[10] content.Code: %d\n", (int)&content.DASType - (int)&content.Code);
    printf("Sizeof char[10] content.DASType: %d\n", (int)&content.wlen - (int)&content.DASType);
    printf("Sizeof short content.wlen:  %d\n", (int)&content.VLtd - (int)&content.wlen);
    printf("Sizeof float content.VLtdL %d\n", (int)&content.samp - (int)&content.VLtd);
    printf("Sizeof int content.samp: %d\n", (int)&content.comp - (int)&content.samp);
    printf("Sizeof int content.comp: %d\n", (int)&content.locationID - (int)&content.comp);
    printf("Sizeof int content.locationID: %d\n", (int)&content.TranMode - (int)&content.locationID);
    printf("Sizeof short content.TranMode: %d\n", (int)&content.TranIns - (int)&content.TranMode);
    printf("Sizeof char[12] content.TranIns: %d\n", (int)&content.TimerMode - (int)&content.TranIns);
    printf("Sizeof short content.TimerMode: %d\n", (int)&content.ClkType - (int)&content.TimerMode);
    printf("Sizeof char[12] content.ClkType: %d\n", (int)&content.ClkErr - (int)&content.ClkType);
    printf("Sizeof float content.ClkErr: %d\n", (int)&content.lat - (int)&content.ClkErr);
    printf("Sizeof float content.lat: %d\n", (int)&content.lon - (int)&content.lat);
    printf("Sizeof floatcontent.lon: %d\n", (int)&content.alt - (int)&content.lon);
    printf("Sizeof floatcontent.alt: %d\n", (int)&content.azimuth - (int)&content.alt);
    printf("Sizeof floatcontent.azimuth: %d\n", (int)&content.incident - (int)&content.azimuth);
    printf("Sizeof floatcontent.incident: %d\n", (int)&content.weight - (int)&content.incident);
    printf("Sizeof short content.weight: %d\n", (int)&content.veloc - (int)&content.weight);
    printf("Sizeof short content.veloc: %d\n", (int)&content.oritype - (int)&content.veloc);
    printf("Sizeof int content.oritype: %d\n", (int)&content.seismometer - (int)&content.oritype);
    printf("Sizeof char[12] content.seismometer: %d\n", (int)&content.sens - (int)&content.seismometer);
    printf("Sizeof double content.sens: %d\n", (int)&content.start_time - (int)&content.sens);
    printf("Sizeof TIME content.start_time: %d\n", (int)&content.record_samples - (int)&content.start_time);
    printf("Sizeof int content.record_samples: %d\n", sizeof(content.record_samples));

    getchar();
    return 0;
}

的输出如下所示：

The output is as follows:

Sizeof int content.no: 4
Sizeof char[20] content.name: 20
Sizeof char[10] content.Code: 10
Sizeof char[10] content.DASType: 10
Sizeof short content.wlen:  4
**Sizeof float content.VLtdL 4**
Sizeof int content.samp: 4
Sizeof int content.comp: 4
Sizeof int content.locationID: 4
Sizeof short content.TranMode: 2
Sizeof char[12] content.TranIns: 12
Sizeof short content.TimerMode: 2
Sizeof char[12] content.ClkType: 12
Sizeof float content.ClkErr: 4
Sizeof float content.lat: 4
Sizeof floatcontent.lon: 4
Sizeof floatcontent.alt: 4
Sizeof floatcontent.azimuth: 4
Sizeof floatcontent.incident: 4
Sizeof short content.weight: 2
Sizeof short content.veloc: 2
Sizeof int content.oritype: 4
Sizeof char[12] content.seismometer: 12
Sizeof double content.sens: 8
Sizeof TIME content.start_time: 12
Sizeof int content.record_samples: 4

编译器是MSVC8，没有定义UNI code，定义没有其他的宏。这是86。

The compiler is MSVC8, no UNICODE defined, no other macro defined. It's x86.

我试图编译相同code在gcc版本3.4.4，输出是一样的。
的sizeof短content.wlen：4

I tried to compile the same code in gcc version 3.4.4, the output is the same. Sizeof short content.wlen: 4

谁能解释这样对我？

先谢谢了。

编辑：谢谢回答！我有现在。

Thanks for answering! I have got it now.

推荐答案

简短的回答只是：对准

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