6.2.3 Generating Sources

Autoconf provides a set of macros that can be used to generate test source files. They are written to be language generic, i.e., they actually depend on the current language (see section 6.1 Language Choice) to "format" the output properly.

Macro: AC_LANG_CONFTEST (source)

Save the source text in the current test source file: `conftest.extension' where the extension depends on the current language.

Note that the source is evaluated exactly once, like regular Autoconf macro arguments, and therefore (i) you may pass a macro invocation, (ii) if not, be sure to double quote if needed.

Macro: AC_LANG_SOURCE (source)

Expands into the source, with proper definition of the current location (e.g., `#line 1234 "configure"' in C), and definition of all the AC_DEFINE performed so far.

For instance executing (observe the double quotation!):

AC_INIT(Autoconf Documentation, 2.57, bug-autoconf@gnu.org) AC_DEFINE([HELLO_WORLD], ["Hello, World\n"]) AC_LANG_CONFTEST( [AC_LANG_SOURCE([[const char hw[] = "Hello, World\n";]])]) gcc -E -dD conftest.c -o -

results in:

# 1 "conftest.c" # 1169 "configure" # 1 "confdefs.h" 1 #define PACKAGE_NAME "Autoconf Documentation" #define PACKAGE_TARNAME "autoconf-documentation" #define PACKAGE_VERSION "2.57" #define PACKAGE_STRING "Autoconf Documentation 2.57" #define PACKAGE_BUGREPORT "bug-autoconf@gnu.org" #define HELLO_WORLD "Hello, World\n" # 1170 "configure" 2 const char hw[] = "Hello, World\n";

Macro: AC_LANG_PROGRAM (prologue, body)

Expands into a source file which consists of the prologue, and then body as body of the main function (e.g., main in C). Since it uses AC_LANG_SOURCE, the feature of the latter are available.

For instance:

AC_INIT(Autoconf Documentation, 2.57, bug-autoconf@gnu.org) AC_DEFINE([HELLO_WORLD], ["Hello, World\n"]) AC_LANG_CONFTEST( [AC_LANG_PROGRAM([[const char hw[] = "Hello, World\n";]], [[fputs (hw, stdout);]])]) gcc -E -dD conftest.c -o -

results in:

# 1 "conftest.c" # 1169 "configure" # 1 "confdefs.h" 1 #define PACKAGE_NAME "Autoconf Documentation" #define PACKAGE_TARNAME "autoconf-documentation" #define PACKAGE_VERSION "2.57" #define PACKAGE_STRING "Autoconf Documentation 2.57" #define PACKAGE_BUGREPORT "bug-autoconf@gnu.org" #define HELLO_WORLD "Hello, World\n" # 1170 "configure" 2 const char hw[] = "Hello, World\n"; int main () { fputs (hw, stdout); ; return 0; }

Macro: AC_LANG_CALL (prologue, function)

Expands into a source file which consists of the prologue, and then a call to the function as body of the main function (e.g., main in C). Since it uses AC_LANG_PROGRAMS, the feature of the latter are available.

This function will probably be replaced in the feature by a version which would enable specifying the arguments. The use of this macro is not encouraged, as it violates strongly the typing system.

Macro: AC_LANG_FUNC_LINK_TRY (function)

Expands into a source file which consists of a pseudo use of the function as body of the main function (e.g., main in C): a simple (function pointer) assignment. Since it uses AC_LANG_PROGRAMS, the feature of the latter are available.

As AC_LANG_CALL, this macro is documented only for completeness. It is considered to be severely broken, and in the future will be removed in favor of actual function calls (with properly typed arguments).