Add parseFile utility function

Since parsing toml from file must be a common use-case, parseFile
would be useful for a casual user.

BUG=#32

include/toml/toml.h

@@ -9,6 +9,7 @@
 #include <cstdint>
 #include <cstdio>
 #include <ctime>
+#include <fstream>
 #include <iomanip>
 #include <istream>
 #include <sstream>
@@ -213,6 +214,8 @@ struct ParseResult {
 
 // Parses from std::istream.
 ParseResult parse(std::istream&);
+// Parses a file.
+ParseResult parseFile(const std::string& filename);
 
 // ----------------------------------------------------------------------
 // Declarations for Implementations
@@ -387,6 +390,17 @@ inline ParseResult parse(std::istream& is)
     return ParseResult(std::move(v), std::move(parser.errorReason()));
 }
 
+inline ParseResult parseFile(const std::string& filename)
+{
+    std::ifstream ifs(filename);
+    if (!ifs) {
+        return ParseResult(toml::Value(),
+                           std::string("could not open file: ") + filename);
+    }
+
+    return parse(ifs);
+}
+
 inline std::string format(std::stringstream& ss)
 {
     return ss.str();

src/CMakeLists.txt

@@ -31,6 +31,7 @@ include_directories(../include)
 
 add_executable(parse_stdin parse_stdin.cc)
 add_executable(parse_file parse_file.cc)
+add_executable(parse_file2 parse_file_2.cc)
 
 function(add_toml_test target)
     add_executable(${target}_test ${target}_test.cc)

src/parse_file.cc

@@ -13,10 +13,7 @@ int main(int argc, char* argv[])
         return 1;
     }
 
-    ifstream ifs(argv[1]);
-    // Pass ifs without checking error (to test toml::parse detects and error).
-    // In usual case, I recommend to check ifs state.
-    toml::ParseResult pr = toml::parse(ifs);
+    toml::ParseResult pr = toml::parseFile(argv[1]);
     if (pr.valid()) {
         cout << pr.value;
     } else {

src/parse_file_2.cc

@@ -0,0 +1,25 @@
+#include "toml/toml.h"
+
+#include <fstream>
+#include <iostream>
+
+using namespace std;
+
+int main(int argc, char* argv[])
+{
+    if (argc < 2) {
+        cerr << "Usage:" << endl
+             << "  " << argv[0] << " <input-file>" << endl;
+        return 1;
+    }
+
+    ifstream ifs(argv[1]);
+    // Pass ifs without checking error (to test toml::parse detects and error).
+    // In usual case, I recommend to check ifs state.
+    toml::ParseResult pr = toml::parse(ifs);
+    if (pr.valid()) {
+        cout << pr.value;
+    } else {
+        cout << pr.errorReason << endl;
+    }
+}