Part 3 - linux

linux-pt3/lib/Makefile

+all:
+	g++ -Wall -fPIC -shared -Wl,-soname,libmymath -Wl,-init,init mymath.cpp -o libmymath.so.1.0 -lc
+

linux-pt3/lib/mymath.cpp

+#include <iostream>
+#include "mymath.h"
+
+void init() {
+	printf("Initializing mymath\n");
+}
+
+void destroy(){
+	printf("Destroying mymath\n");
+}
+
+int add(int x, int y){
+	std::cout << "Adding\n";
+	return x + y;
+}
+
+int sub(int x, int y){
+	std::cout << "Subtracting\n";
+	return x - y;
+}
+

linux-pt3/lib/mymath.h

+extern "C" void init() __attribute__((constructor));
+extern "C" void destroy() __attribute__((destructor));
+extern "C" int add(int, int);
+extern "C" int sub(int, int);
+

linux-pt3/progs/linked/Makefile

+all:
+	g++ -Wall -Iinclude -Llib src/main.cpp -lmymath -o bin/test
+

linux-pt3/progs/linked/include/mymath.h

+extern "C" int add(int, int);
+extern "C" int sub(int, int);
+

linux-pt3/progs/linked/output

+Initializing mymath
+Initializing mymath
+Adding
+Mymath adding. 3+4=7
+Subtracting
+Mymath subtracting 3-4=-1
+Destroying mymath

linux-pt3/progs/linked/src/main.cpp

+#include <cstdio>
+#include "mymath.h"
+
+int main(){
+	printf("Mymath adding. 3+4=%d\n", add(3, 4));
+	printf("Mymath subtracting 3-4=%d\n", sub(3, 4));
+	return 0;
+}
+

linux-pt3/progs/loaded/Makefile

+all:
+	g++ -rdynamic -o bin/main src/main.cpp -ldl
+

linux-pt3/progs/loaded/output

+adding 3+4=Adding
+7
+subtracting 3-4=Subtracting
+-1

linux-pt3/progs/loaded/src/main.cpp

+#include <iostream>
+#include <dlfcn.h>
+
+int main() {
+	void* lib_handle;
+	int (*add)(int, int);
+	int (*sub)(int, int);
+
+	lib_handle = dlopen("/usr/local/lib/libmymath.so", RTLD_LAZY);
+	if(!lib_handle) {
+		std::cout << "Did not find libmymath\n";
+		return 1;
+	}
+	add = (int(*)(int, int))dlsym(lib_handle, "add");
+	sub = (int(*)(int, int))dlsym(lib_handle, "sub");
+	if(!add || !sub){
+		std::cerr << "Could not load functions\n";
+		return 2;
+	}
+	std::cout << "adding 3+4=" << (*add)(3, 4) << std::endl;
+	std::cout << "subtracting 3-4=" << (*sub)(3, 4) << std::endl;
+	dlclose(lib_handle);
+	return 0;
+}
+