On Thu, 3 Aug 2000, Christophe TROESTLER wrote: > Thanks to all for answering my very simple question. Now, how was I > supposed to know I had to link against `m'? I mean, given a header > file, is the file I have to link against specified in the doc? Is > there any info on that subject you can refer me to?
Unfortunately there's no one-to-one correspondence between header files and library files. Although every library intended for development will have a header (otherwise you could not compile programs designed to use it), not every header has its own library - a given library can have multiple header files, and some header files aren't associated with any particular library. Anyway, the short answer is that the definitions of functions don't necessarily say what library you have to link to actually get them. You pretty much just have to know, pick it up from looking at other examples... or go rooting around through the libraries looking for it... You can get a list of functions in a library by using nm -C <file>. Those of class 'T' are function calls you can use. (The -C makes it work with C++ functions as well as C functions). "nm -o -C *.a | grep <funcname>" is a good way of finding out which library a given function is in, provided you know which directory the library is in (/usr/lib is a good starting place :} ). Don't forget that when linking you don't specify the 'lib' or the '.a' - for example to link with libm.a you just do -lm, not -llibm.a. Symbols of class 'U' are not defined in this library, but rather are used by this library but located somewhere else. So don't be distracted by those. A library is really a collection of .o object files (see ar for more details). So nm (and other tools) will often tell you what object file within the library is being referred to. Normally, this only matters if you are making your own libraries.
