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__has_embed

As explained in Modern C, Third Edition

__has_embed is a C23 preprocessing feature that tests whether a specified file can be embedded.

__has_embed is a C23 preprocessing feature for testing binary-file embedding. First test whether __has_embed is defined; then call __has_embed("picture.dat") in a preprocessor condition to determine whether that file can be embedded. section 14.6

Guard an embedded initializer

unsigned char logo[] = {\n#if defined(__has_embed) && __has_embed("picture.dat")\n# embed "picture.dat"\n#else\n "embed directive is missing"\n#endif\n};\n\nWhen supported and available, #embed supplies the file's bytes as comma-separated decimal values suitable for initializing logo; otherwise the fallback text is used. section 14.6

How Modern C, Third Edition covers it

How deep it goes
Explains implementation detection and the result value, while leaving byte-list generation to #embed.
Examples
Uses picture.dat to initialize logo and a fallback string when embedding support or the file is unavailable.
What you can do after
Apply it via preprocessor conditions to select embedded binary data or a fallback initializer.
How it connects
Connects __has_embed with #embed directives, preprocessor conditions, binary streams, and array initializers.
Cover of Modern C, Third Edition
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