fixed line numbers for syntax errors by considering removed source lines: labels, comments

interpreter.cpp

@@ -34,10 +34,13 @@ std::string interpreter::eval(std::istream& in, bool& done) {
 
     // first pass: read program & resolve labels
     for (std::string line; std::getline(in, line); ++_pc) {
-        if (line[0] == ':') {
+        if (line[0] == ':') { // check label definition
-            _labels.emplace(line.substr(1), _pc--);
+            _labels.emplace(line.substr(1), _pc);
+            _pc_offsets.push_back(_pc);
+            _pc--; // we'll lose this line
         } else if (line[0] == '#') { // check comment
-            _pc--;
+            _pc_offsets.push_back(_pc);
+            _pc--; // we'll lose this line
         } else {
             _prog.push_back(line);
         }
@@ -126,7 +129,11 @@ void interpreter::exec_instruction(const std::string& code, bool& done) {
     else if (code == "inp") inp();
     else if (code == "out") out();
     else if (code == "err") err();
-    else throw syntax_error {code, _pc + 1};
+    else {
+        auto it = std::upper_bound(_pc_offsets.begin(), _pc_offsets.end(), _pc);
+        size_t lineno {it - _pc_offsets.begin() + _pc + 1};
+        throw syntax_error {code, lineno};
+    }
 }
 
 // integer operations -----------------------------------------------------

interpreter.hpp

@@ -38,6 +38,7 @@ class interpreter {
         std::map<std::string, std::string> _vars;
         std::vector<int> _calls;
         std::vector<std::string>::size_type _pc {0};
+        std::vector<size_t> _pc_offsets;
 
         void reset();
         void exec_instruction(const std::string& code, bool& done);