Fixes https://github.com/lemire/fast_float/issues/19

include/fast_float/ascii_number.h

@@ -115,8 +115,8 @@ parsed_number_string parse_number_string(const char *p, const char *pend, chars_
   int32_t digit_count =
       int32_t(p - start_digits - 1); // used later to guard against overflows
  
-  if ((p != pend) && (('e' == *p) || ('E' == *p))) {
+  if ((fmt & chars_format::scientific) && (p != pend) && (('e' == *p) || ('E' == *p))) {
-    if((fmt & chars_format::fixed) && !(fmt & chars_format::scientific)) { return answer; } 
+    const char * location_of_e = p;
     int64_t exp_number = 0;            // exponential part
     ++p;
     bool neg_exp = false;
@@ -127,17 +127,23 @@ parsed_number_string parse_number_string(const char *p, const char *pend, chars_
       ++p;
     }
     if ((p == pend) || !is_integer(*p)) {
-      return answer;
+      if(!(fmt & chars_format::fixed)) {
-    }
+        // We are in error.
-    while ((p != pend) && is_integer(*p)) {
+        return answer;
-      uint8_t digit = uint8_t(*p - '0');
-      if (exp_number < 0x10000) {
-        exp_number = 10 * exp_number + digit;
       }
-      ++p;
+      // Otherwise, we will be ignoring the 'e'.
+    } else {
+      while ((p != pend) && is_integer(*p)) {
+        uint8_t digit = uint8_t(*p - '0');
+        if (exp_number < 0x10000) {
+          exp_number = 10 * exp_number + digit;
+        }
+        ++p;
+      }
+      exponent += (neg_exp ? -exp_number : exp_number);
     }
-    exponent += (neg_exp ? -exp_number : exp_number);
   } else {
+    // If it scientific and not fixed, we have to bail out.
     if((fmt & chars_format::scientific) && !(fmt & chars_format::fixed)) { return answer; }
   }
   answer.lastmatch = p;

include/fast_float/parse_number.h

@@ -63,6 +63,7 @@ from_chars_result parse_infnan(const char *first, const char *last, T &value)  n
     }
   }
   answer.ec = std::errc::invalid_argument;
+  answer.ptr = first;
   return answer;
 }
 } // namespace

tests/basictest.cpp

@@ -147,9 +147,42 @@ bool issue8() {
   return true;
 }
 
+bool check_behavior() {
+    const std::string input =  "abc";
+    double result;
+    auto answer = fast_float::from_chars(input.data(), input.data()+input.size(), result);
+    if(answer.ec != std::errc()) {
+      std::cerr << "parsing failure as expected\n";
+      // specification says ptr should point at first
+      if(answer.ptr != input.data()) {
+        std::cerr << "If there is no pattern match, we should have ptr equals first\n";
+        return false;
+      }
+      return true;
+    }
+    std::cout << "parsed the number " << result << std::endl;
+    return false;
+}
+
+bool issue19() {
+    const std::string input =  "3.14e";
+    double result;
+    auto answer = fast_float::from_chars(input.data(), input.data()+input.size(), result);
+    if(answer.ec != std::errc()) {
+      std::cerr << "We want to parse up to 3.14\n";
+      return false;
+    }
+    std::cout << "parsed the number " << result << std::endl;
+    if(answer.ptr != input.data() + 4) {
+      std::cout << "Parsed the number and stopped at the right character." << result << std::endl;
+      return true;
+    }
+    return false;
+}
+
 int main() {
-
+  Assert(issue19());
-
+  Assert(check_behavior());
   std::cout << "======= 64 bits " << std::endl;
   Assert(basic_test_64bit("INF",std::numeric_limits<double>::infinity()));
   Assert(basic_test_64bit("-INF",-std::numeric_limits<double>::infinity()));