#pragma预处理实例

1.#include <stdio.h>

#if defined(ANDROID20)
    #pragma message("Compile Android SDK 2.0...")
    #define VERSION "Android 2.0"
#elif defined(ANDROID23)
    #pragma message("Compile Android SDK 2.3...")
    #define VERSION "Android 2.3"
#elif defined(ANDROID40)
    #pragma message("Compile Android SDK 4.0...")
    #define VERSION "Android 4.0"
#else
    #error Compile Version is not provided!
#endif

int main()
{
    printf("%s\n", VERSION);

    return 0;
}

2.#include <stdio.h>

#pragma pack(8)

struct S1
{
    short a;
    long b;
};

struct S2
{
    char c;
    struct S1 d;
    double e;
};

#pragma pack()

int main()
{
    struct S2 s2;
    
    printf("%d\n", sizeof(struct S1));
    printf("%d\n", sizeof(struct S2));
    printf("%d\n", (int)&(s2.d) - (int)&(s2.c));

    return 0;
}