Error message conflicts with my assumption

Question

if i saw below error message
it will drive me to think about didnot provide library which has defination
of alloc function. or .cpp file which defines alloca function is missing
but real error is alloca.h header file is missing. once i include header file alloca.h. then it compiles and links
i think if header file is missing , error message should be alloca has no prototype.
could could tell me why?
/sapmnt/global/tools/compiler/WS6U2/SUNWspro/bin/CC -xarch=v9 -ldl -g -KPIC -mt -o agate w3xxmain.o sapcpp45.so xml63d.so sapbasis20.so sappmon.so sapagate.so sapxgdk.so libsapu16_mt.so
ild: (undefined symbol) alloca -- referenced in /data2/c5040606/build/gnu_regex.so

Answer 1

Alloca () is a special function in that , to get the compiler builtin version of alloca, you have to include alloca.h in Sun compiler environment. My guess is when you built gnu_regex.so, you must have provided a prototype for alloca without including alloca.h. The behavior will be you get a reference to alloa() , not
__builtin_allcoca() , the builtin version recognised by the compiler itself. But if there is no prototype for alloca in your code and you didn't inlcude alloca.h, you should get the error (no prototype).
-Ananth