Memory Alignment and Struct Padding

Snippet

Memory Alignment and Struct Padding

CPUs often access memory in multi-byte chunks (word size). To optimize access, compilers align structure members to specific boundaries. This results in 'padding'—wasted space between members. Expert developers reorder structure members from largest alignment requirement to smallest to minimize memory footprint and improve cache efficiency.

snippet.c
c
struct Optimized {
    double a;      // 8 bytes
    int b;         // 4 bytes
    char c;        // 1 byte
    char _pad[3];  // 3 bytes implicit padding
}; // Total 16 bytes

Breakdown

double a;

Requires 8-byte alignment on most 64-bit systems.

char _pad[3];

Implicit bytes added to ensure the total struct size is a multiple of the largest alignment.

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Memory Alignment and Struct Padding

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