Improve example code

README.md

@@ -1,35 +1,38 @@
 # [hmac_sha256](https://github.com/h5p9sl/hmac_sha256)
 A SHA256 HMAC implementation in C/C++
 
-## Example (C++)
+## Usage Example (C++)
 ```cpp
 #include "hmac_sha256.h"
 
-#include <iostream>
-#include <sstream>
 #include <vector>
 #include <string>
-#include <cstring>
-#include <tuple>
+#include <iostream>
+#include <sstream>
 
-int main(void) {
+#define SHA256_HASHLEN 32
+
+int main() {
     const std::string testvector = "b0344c61d8db38535ca8afceafbf12b881dc20c9833da726e9376c2e32cff7";
+    const std::string str_data = "Hi There";
+
     std::vector<uint8_t> key, data, out;
     std::stringstream result;
 
     // Allocate memory
-    key.resize(20);
-    data.resize(8);
-    out.resize(32);
+    key.resize(20, 0x0b);
+    data.resize(str_data.length(), 0);
+    out.resize(SHA256_HASHLEN, 0);
 
-    // Initialize variables
-    strncpy((char*)data.data(), "Hi There", data.size());
-    memset(key.data(), 0x0b, key.size());
+    // Fill data
+    data.assign(str_data.cbegin(), str_data.cend());
 
     // Call hmac sha256 function
-    hmac_sha256(key.data(), key.size(),
+    hmac_sha256(
+        key.data(),  key.size(),
         data.data(), data.size(),
-            out.data(), out.size());
+        out.data(),  out.size()
+    );
 
     // Convert 'out' to string
     for (unsigned i = 0; i < out.size(); i++) {
@@ -41,9 +44,9 @@ int main(void) {
     // Compare result
     if (testvector.compare(result.str()) == 0) {
         std::cout << "Test passed!" << std::endl;
-        return 0;
-    }
+    } else {
         std::cout << "Test failed." << std::endl;
+    }
 
     return 0;
 }