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copied!<blockquote> <p>This is prompted by a an answer I gave to a current question which asks about a generics library for C - the questioner specifically states that they do not want to use C++.</p> </blockquote> <p>C is a complete programming language. C is not an arbitrary subset of C++. C is not a subset of C++ at all. </p> <p>This is valid C:</p> <pre><code>foo_t* foo = malloc ( sizeof(foo_t) ); </code></pre> <p>To make it compile as C++ you have to write:</p> <pre><code>foo_t* foo = static_cast<foo_t*>( malloc ( sizeof(foo_t) ) ); </code></pre> <p>which isn't valid C any more. (you could use the C-style cast, it which case it would compile in C, but be shunned by most C++ coding standards, and also by many C programmers; witness the "don't cast malloc" comments all over Stack Overflow).</p> <hr> <p>They are not the same language, and if you have an existing project in C you don't want to rewrite it in a different language just to use a library. You would prefer to use libraries which you can interface to in the language you are working in. (In some cases this is possible with a few <code>extern "C"</code> wrapper functions, depending on how template/inline a C++ library is.)</p> <p>Taking the first C file in a project I'm working on, this is what happens if you just swap <code>gcc std=c99</code> for <code>g++</code>:</p> <pre><code>sandiego:$ g++ -g -O1 -pedantic -mfpmath=sse -DUSE_SSE2 -DUSE_XMM3 -I src/core -L /usr/lib -DARCH=elf64 -D_BSD_SOURCE -DPOSIX -D_ISOC99_SOURCE -D_POSIX_C_SOURCE=200112L -Wall -Wextra -Wwrite-strings -Wredundant-decls -Werror -Isrc src/core/kin_object.c -c -o obj/kin_object.o | wc -l In file included from src/core/kin_object.c:22: src/core/kin_object.h:791:28: error: anonymous variadic macros were introduced in C99 In file included from src/core/kin_object.c:26: src/core/kin_log.h:42:42: error: anonymous variadic macros were introduced in C99 src/core/kin_log.h:94:29: error: anonymous variadic macros were introduced in C99 ... cc1plus: warnings being treated as errors src/core/kin_object.c:101: error: ISO C++ does not support the ‘z’ printf length modifier .. src/core/kin_object.c:160: error: invalid conversion from ‘void*’ to ‘kin_object_t*’ .. src/core/kin_object.c:227: error: unused parameter ‘restrict’ .. src/core/kin_object.c:271: error: ISO C++ does not support the ‘z’ printf length modifier src/core/kin_object.c:271: error: ISO C++ does not support the ‘z’ printf length modifier </code></pre> <p>In total 69 lines of errors, four of which are invalid conversions, but mostly for features that exist in C99 but not in C++.</p> <p>It's not like I'm using those features for the fun of it. It would take significant work to port it to a different language.</p> <p>So it is plain wrong to suggest that </p> <blockquote> <p>[a] C compiler is almost certainly really a C++ compiler, so there are no software cost implications </p> </blockquote> <p>There are often significant cost implications in porting existing C code to the procedural subset of C++.</p> <p>So suggesting <em>'use the C++ std::queue class'</em> as an answer to question looking for an library implementation of a queue in C is dafter than suggesting <em>'use objective C'</em> and <em>'call the Java java.util.Queue class using JNI'</em> or <em>'call the CPython library'</em> - Objective C actually is a proper superset of C (including C99), and Java and CPython libraries both are callable directly from C without having to port unrelated code to the C++ language. </p> <p>Of course you could supply a C façade to the C++ library, but once you're doing that C++ is no different to Java or Python. </p>

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