How Can I Compile Anonymous Structs/Unions in C with GCC?

Compiling C Code with Anonymous Structs/Unions

Anonymous structs and unions allow for flexible data structures without having to declare a separate struct/union type. In C , anonymous structs/unions can be created using nested structs and unions; however, C does not provide direct support for this functionality.

To achieve similar functionality in C with GCC, you can use the -fms-extensions flag. This flag enables Microsoft-style extensions, including support for anonymous structs/unions.

For example, consider the following code:

<code class="c">typedef struct {
    union {
        struct {
            float x, y, z;
        };
        float xyz[3];
    };
} Vector3;</code>

With the addition of the -fms-extensions flag, the code compiles successfully with the following command:

gcc -fms-extensions -c <source_file>.c

This extension allows you to access the anonymous struct members through the array members, as in the following code:

<code class="c">Vector3 v;
assert(&v.xyz[0] == &v.x);
assert(&v.xyz[1] == &v.y);
assert(&v.xyz[2] == &v.z);</code>

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