Hi, After perusing the draft of C99 [1], which is the closest to the default -std in GCC 4.7.2 (I believe the default is C90), I think your code does not compile because it has an undefined behavior, which according to section 3.4.3 paragraph 2 can result in a compilation error. To quote the said paragraph, possible undefined behavior ranges from ignoring the situation completely with unpredictable results, to behaving during translation or program execution in a documented manner characteristic of the environment (with or without the issuance of a diagnostic message), to terminating a translation or execution (with the issuance of a diagnostic message). End quote. The undefined behavior is due to function bar having both an external linkage as per section 6.2.2 paragraph 4 and an internal linkage as per section 6.2.2 paragraph 3. To quote section 6.2.2 paragraph 7, if, within a translation unit, the same identifier appears with both internal and external linkage, the behavior is undefined. End quote. [1] http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf -- Best regards, Tadeus On Fri, Feb 16, 2018 at 4:14 PM, Tadeus Prastowo <tadeus.prastowo@xxxxxxxx> wrote: > Hi, > > I think you are referring to C89 standard. Newer version of GCC might > have switched to newer version of the C standard. So, try to compile > your code with -std=c89? > > -- > Best regards, > Tadeus > > > On Fri, Feb 16, 2018 at 3:41 PM, Andrew Makhorin <mao@xxxxxxx> wrote: >> Hello, >> >> On compiling the following code with gcc (Debian 4.7.2-5) 4.7.2: >> >> int foo(int x, int y) >> { >> extern int bar(); >> return bar(x, y); >> } >> >> static int bar(int x, int y) >> { >> return x + y; >> } >> >> I get the following error: >> >> mao@corvax:~/Desktop$ gcc -c test.c >> test.c:7:15: error: static declaration of 'bar' follows non-static >> declaration >> test.c:3:21: note: previous declaration of 'bar' was here >> >> However, the Standard says [6.1.2.2 Linkages of identifiers]: >> >> If the declaration of an identifier for an object or a function >> contains the storage-class specifier extern, the identifier has the >> same linkage as any visible declaration of the identifier with file >> scope. >> >> There is no other way to declare 'bar' as static in block scope, >> because it is a function, so this error confuses me. Could anyone >> explain this? Should it be a warning rather than error? I'd like to note >> that my code is compiled successfully with older versions of gcc and >> with many other C compilers. >> >> >> Thanks, >> >> Andrew Makhorin >> >>
