Avoid need to change program.c by providing lib name. (#55)

* Avoid need to change program.c by providing name.

Changes juliac.jl to provide the name of the created shared lib
("libhello") to the c preprocessor as a macro, via "-D".

This way you do not need to modify the provided program.c when compiling
a new julia program.

Addresses issue #3.

* fix: Also use macro for libname in program2.c

* Update README to reflect macro defined libname.

Remove references from README to changing the image name manually in
`program.c`. Add note about the availability of the image lib name in
the C preprocessor macro.

* Rename lib-name macro variable; remove default val.

s/JULIA_LIB_NAME/JULIAC_JL_PROGRAM_LIBNAME/g;
Remove default value. The libname *must* be provided on the commandline
via `-DJULIAC_JL_PROGRAM_LIBNAME="libname"`.

Author: NHDaly

README.md

@@ -97,13 +97,11 @@ script into object code, and then builds it into the system image
 specified by the `-J` switch. This prepares an object file, which is
 then linked into a shared library containing the system image and user
 code. A driver script such as the one in `program.c` can then be used to
-build a binary that runs the julia code. For now, the image file has
-to be changed in `program.c` to match the name of the shared library
-containing the compiled julia program.
+build a binary that runs the julia code.
 
 Instead of a driver script, the generated system image can be embedded
 into a larger program following the embedding examples and relevant
-sections in the Julia manual.
+sections in the Julia manual. Note that the name of the generated system image (`"libhello"` for `hello.jl`) is accessible from C in the preprocessor macro `JULIAC_PROGRAM_LIBNAME`.
 
 With Julia 0.7, a single large binary can be created, which does not
 require the driver program to load the shared library. An example of

juliac.jl

@@ -250,6 +250,7 @@ function julia_compile(julia_program, c_program=nothing, build_dir="builddir", v
     end
 
     if executable
+        push!(cflags, "-DJULIAC_PROGRAM_LIBNAME=\"lib$julia_program_basename\"")
         command = `$cc -m64 -o $e_file $c_program $s_file $cflags $ldflags $ldlibs`
         if is_apple()
             command = `$command -Wl,-rpath,@executable_path`

program.c

@@ -22,7 +22,8 @@ int main(int argc, char *argv[])
     // Initialize Julia
     uv_setup_args(argc, argv); // no-op on Windows
     libsupport_init();
-    jl_options.image_file = "libhello";
+    // JULIAC_PROGRAM_LIBNAME defined on command-line for compilation.
+    jl_options.image_file = JULIAC_PROGRAM_LIBNAME;
     julia_init(JL_IMAGE_JULIA_HOME);
 
     // Do some work

program2.c

@@ -41,7 +41,8 @@ int wmain(int argc, wchar_t *wargv[], wchar_t *envp[])
     // initialization
     libsupport_init();
     // jl_options.compile_enabled = JL_OPTIONS_COMPILE_OFF;
-    jl_options.image_file = "libhello";
+    // JULIAC_PROGRAM_LIBNAME defined on command-line for compilation.
+    jl_options.image_file = JULIAC_PROGRAM_LIBNAME;
     julia_init(JL_IMAGE_JULIA_HOME);
 
     // build arguments array: `String[ unsafe_string(argv[i]) for i in 1:argc ]`