#pragma pack(n)

Where:

The default is #pragma pack(8).

This example demonstrates how pack(2) aligns integer variable b to a 2-byte boundary.

typedef struct
{ 
    char a;
    int b;
} S;

#pragma pack(2)

typedef struct
{ 
    char a;
    int b;
} SP;

S var = { 0x11, 0x44444444 };
SP pvar = { 0x11, 0x44444444 };

The layout of S is as shown in Figure 4.1, while the layout of SP is as shown in Figure 4.2. In Figure 4.2, x denotes one byte of padding.