How Can I Programmatically Detect Endianness in C ?

Detecting Endianness in C

Endianness, which refers to the order in which bytes are stored in memory, can vary between different architectures. In C , programmers may need to determine the endianness of the system they are running on to ensure compatibility with underlying hardware or data structures.

To programmatically detect endianness, one method involves inspecting the byte representations of specific data types. The following code snippet demonstrates how this approach works:

union Data {
    uint32_t i;
    char c[4];
};

bool is_big_endian()
{
    Data data = {0x01020304};
    return data.c[0] == 1;
}

In this code, a union is defined where the first member is an unsigned 32-bit integer (uint32_t) and the second member is an array of four characters (c[4]). When assigning the value 0x01020304 to the union member i, the byte representations of the integer are placed in the c array elements in reverse order (little-endian) or normal order (big-endian), depending on the system's endianness.

By checking the value of c[0], we can determine the endianness: if c[0] contains the least significant byte (lower value), the system is little-endian; if c[0] contains the most significant byte (higher value), the system is big-endian.

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