c - 为什么 short 在 C 的结构中存储为 4 个字节？

Question

我有以下两个结构:

问题是 sizeof(Content) 返回 160。该结构由 11 个短整型、6 个整型、76 个字符、7 个浮点型、1 个 double 型组成，共计 158 个字节。我数了三遍，还是相差2个字节。

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;

我写了一小段代码来打印每个变量在结构中的位置，突然发现float wlen 占用了 4 个字节。我的代码如下:

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;
}

输出如下:

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UNICODE，也没有定义其他宏。它是 x86。

我尝试在 gcc 3.4.4 版本中编译相同的代码，输出是相同的。 Sizeof short content.wlen: 4

谁能给我解释一下？

提前致谢。

编辑:感谢您的回答!我现在明白了。

Answer 1

仅简短回答:alignment