C preprocessor: Difference between revisions

Revision as of 08:17, 27 August 2025

Latest revision as of 19:20, 28 August 2025

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==== Binary resource inclusion ====

[[C23 (C standard revision)|C23]] and [[C++26]] introduce the <code>#embed</code> directive for '''binary resource inclusion''' which allows including the content of a binary file into a source even thoughif it's is not valid C code.<ref>{{cite web |title=WG14-N3017 : #embed – a scannable, tooling-friendly binary resource inclusion mechanism |url=https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3017.htm |website=open-std.org |archive-url=https://web.archive.org/web/20221224045304/https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3017.htm |archive-date=24 December 2022 |date=2022-06-27 |url-status=live}}</ref><ref>{{Cite web|title=#embed - a scannable, tooling-friendly binary resource inclusion mechanism|url=https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2025/p1967r14.html|website=open-std.org }}</ref>

This allows binary resources (like images) to be included into a program without requiring processing by external tools like <code>xxd -i</code> and without the use of [[string literal]]s which have a length limit on [[MSVC]]. Similarly to <code>xxd -i</code> the directive is replaced by a comma separated list of integers corresponding to the data of the specified resource. More precisely, if an array of type {{code|unsigned char}} is initialized using an <code>#embed</code> directive, the result is the same as-if the resource was written to the array using <code>[[fread]]</code> (unless a parameter changes the embed element width to something other than <code>[[Limits.h|CHAR_BIT]]</code>). Apart from the convenience, <code>#embed</code> is also easier <!--than what?--> for compilers to handle, since they are allowed to skip expanding the directive to its full form due to the [[as-if rule]].

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<syntaxhighlight lang="cpp">

const unsigned char icon_display_dataiconDisplayData[] = {

#embed "art.png"

};

/* specify any type which can be initialized form integer constant expressions will do */

const char reset_blobresetBlob[] = {

#embed "data.bin"

};

/* attributes work just as well */

const signed char aligned_data_stralignedDataString[] __attribute__ ((aligned (8))) = {

#embed "attributes.xml"

};