cat > test.c
#include <stdio.h>
#include <stdlib.h>
#include <dlfcn.h>
#define LIBM_SO "liba.so"
int
main(void)
{
void *handle;
double (*cosine)(double);
char *error; handle = dlopen(LIBM_SO, RTLD_LAZY);
if (!handle) {
fprintf(stderr, "%s\n", dlerror());
exit(EXIT_FAILURE);
}
dlerror(); /* Clear any existing error */
cosine = (double (*)(double)) dlsym(handle, "cos");
/* According to the ISO C standard, casting between function
pointers and 'void *', as done above, produces undefined results.
POSIX.1-2001 and POSIX.1-2008 accepted this state of affairs and
proposed the following workaround:
*(void **) (&cosine) = dlsym(handle, "cos");
This (clumsy) cast conforms with the ISO C standard and will
avoid any compiler warnings.
The 2013 Technical Corrigendum 1 to POSIX.1-2008 improved matters
by requiring that conforming implementations support casting
'void *' to a function pointer. Nevertheless, some compilers
(e.g., gcc with the '-pedantic' option) may complain about the
cast used in this program. */
error = dlerror();
if (error != NULL) {
fprintf(stderr, "%s\n", error);
exit(EXIT_FAILURE);
}
printf("%f\n", (*cosine)(2.0));
dlclose(handle);
exit(EXIT_SUCCESS);
}
gcc -static test.c -ld
/usr/bin/ld: /tmp/ccpQ2mA7.o: в функции «main»:
test2.c:(.text+0x15): предупреждение: Using 'dlopen' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking
Вариант для распечатки
