Add an example of how to link to libsnark.so

Issue #18

README.md

@@ -262,6 +262,7 @@ with some (currently sparse) comments, install the `doxygen` and `graphviz` pack
 
 To develop an application that uses libsnark, you could add it within the libsnark directory tree and adjust the Makefile, but it is far better to build libsnark as a (shared or static) library. You can then write your code in a separate directory tree, and link it against libsnark.
 
+See a full example in ./link_example.
 
 To build just the shared object library `libsnark.so`, run:
 

link_example/Makefile

@@ -0,0 +1,10 @@
+# Set this to the directory where you installed libsnark.
+# If you install to linker_example (`make install PREFIX=linker_example`),
+# the default prefix will work.
+INSTALL_PREFIX=.
+
+all:
+	$(CXX) main.cpp -o main -std=c++11 -L$(INSTALL_PREFIX)/lib -lsnark -lsupercop -lgmp -lgmpxx -I$(INSTALL_PREFIX)/include -I$(INSTALL_PREFIX)/include/libsnark -DCURVE_BN128
+
+run:
+	LD_LIBRARY_PATH=$(INSTALL_PREFIX)/lib ./main

link_example/main.cpp

@@ -0,0 +1,11 @@
+#include <iostream>
+
+#include <gadgetlib2/examples/simple_example.hpp>
+#include <zk_proof_systems/ppzksnark/r1cs_ppzksnark/examples/run_r1cs_ppzksnark.hpp>
+
+int main() {
+    const libsnark::r1cs_example<libsnark::Fr<libsnark::default_ec_pp> > example = libsnark::gen_r1cs_example_from_gadgetlib2_protoboard(100);
+    const bool test_serialization = true;
+    const bool bit = libsnark::run_r1cs_ppzksnark<libsnark::default_ec_pp>(example, test_serialization);
+    std::cout << (bit ? "Success" : "Failure") << std::endl;
+}