Added integer parsing functions in base/string_to_number.h

webrtc/base/string_to_number.h

+/*
+ *  Copyright 2017 The WebRTC Project Authors. All rights reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#ifndef WEBRTC_BASE_STRING_TO_NUMBER_H_
+#define WEBRTC_BASE_STRING_TO_NUMBER_H_
+
+#include <string>
+#include <limits>
+
+#include "webrtc/base/optional.h"
+
+namespace rtc {
+
+// This file declares a family of functions to parse integers from strings.
+// The standard C library functions either fail to indicate errors (atoi, etc.)
+// or are a hassle to work with (strtol, sscanf, etc.). The standard C++ library
+// functions (std::stoi, etc.) indicate errors by throwing exceptions, which
+// are disabled in WebRTC.
+//
+// Integers are parsed using one of the following functions:
+//   rtc::Optional<int-type> StringToNumber(const char* str, int base = 10);
+//   rtc::Optional<int-type> StringToNumber(const std::string& str,
+//                                          int base = 10);
+//
+// These functions parse a value from the beginning of a string into one of the
+// fundamental integer types, or returns an empty Optional if parsing
+// failed. Values outside of the range supported by the type will be
+// rejected. The strings must begin with a digit or a minus sign. No leading
+// space nor trailing contents are allowed.
+// By setting base to 0, one of octal, decimal or hexadecimal will be
+// detected from the string's prefix (0, nothing or 0x, respectively).
+// If non-zero, base can be set to a value between 2 and 36 inclusively.
+//
+// If desired, this interface could be extended with support for floating-point
+// types.
+
+namespace string_to_number_internal {

[kwiberg-webrtc, 2017/02/20 13:27:20]

Bonus points for the very specific internal namespace name!

[ossu, 2017/02/20 14:09:06]

Thanks! :)

+rtc::Optional<long long int> ParseSigned(const char* str, int base);

[kwiberg-webrtc, 2017/02/20 13:27:20]

Just "long long" means the same thing as "long long int", right? And it's not
quite as long...

[ossu, 2017/02/20 14:09:06]

Done.

+rtc::Optional<unsigned long long int> ParseUnsigned(const char* str, int base);
+}  // namespace string_to_number_internal
+
+template <typename T>
+typename std::enable_if<std::is_integral<T>::value && std::is_signed<T>::value,
+                        rtc::Optional<T>>::type
+StringToNumber(const char* str, int base = 10) {
+  static_assert(std::numeric_limits<T>::max() <=
+                std::numeric_limits<long long int>::max() &&
+                std::numeric_limits<T>::lowest() >=
+                std::numeric_limits<long long int>::lowest(),
+                "StringToNumber only supports signed integers as large as "
+                "long long int");

[kwiberg-webrtc, 2017/02/20 13:27:20]

Multi-line string literals are a bit easier to read if you have leading instead
of trailing spaces (since the left but not the right margin tends to be
aligned).

[ossu, 2017/02/20 14:09:06]

I'm not sure I agree and clang-format seems to split strings like this. I've
rejiggered them a bit, though, so they should be a bit easier to read. They also
fit better with the shorter type names. I chose not to change the type name in
the message, since I find it made the message flow strangely.

[kwiberg-webrtc, 2017/02/20 16:51:26]

Acknowledged. Not everyone can be right all the time.

+  rtc::Optional<long long int> value =
+      string_to_number_internal::ParseSigned(str, base);
+  if (value && *value >= std::numeric_limits<T>::min() &&
+      *value <= std::numeric_limits<T>::max()) {

[kwiberg-webrtc, 2017/02/20 13:27:20]

If you pass the min and max value to the internal parse function, you can do
this check there---that'll mean less code to inline everywhere. Not sure if it's
worth it, though; you decide.

[ossu, 2017/02/20 14:09:06]

I think this is clearer - we'll need to do a cast anyway, so it's nice to ensure
the range is good in the same place.

[kwiberg-webrtc, 2017/02/20 16:51:26]

Acknowledged.

+    return rtc::Optional<T>(static_cast<T>(*value));

[kwiberg-webrtc, 2017/02/20 13:27:20]

This ought to be dchecked_cast, but I won't request that you write that before
landing this CL... :-)

[ossu, 2017/02/20 14:09:06]

I didn't find that one. Found a checked_cast, though, but it seems to do what
I'm already doing on the previous line, so I don't think it's necessary.

[kwiberg-webrtc, 2017/02/20 16:51:26]

Yes, we only have checked_cast. dchecked_cast doesn't exist yet, but should...

+  }
+  return rtc::Optional<T>();
+}
+
+template <typename T>
+typename std::enable_if<std::is_integral<T>::value &&
+                            std::is_unsigned<T>::value,
+                        rtc::Optional<T>>::type
+StringToNumber(const char* str, int base = 10) {
+  static_assert(
+      std::numeric_limits<T>::max() <=
+          std::numeric_limits<unsigned long long int>::max(),
+      "StringToNumber only supports unsigned integers as large as unsigned "
+      "long long int");
+  rtc::Optional<unsigned long long int> value =
+      string_to_number_internal::ParseUnsigned(str, base);
+  if (value && *value <= std::numeric_limits<T>::max()) {
+    return rtc::Optional<T>(static_cast<T>(*value));
+  }
+  return rtc::Optional<T>();
+}
+
+// The std::string overloads only exists if there is a matching const char*
+// version.
+template <typename T>
+auto StringToNumber(const std::string& str, int base = 10)
+    -> decltype(StringToNumber<T>(str.c_str(), base)) {
+  return StringToNumber<T>(str.c_str(), base);
+}
+
+}  // namespace rtc
+
+#endif  // WEBRTC_BASE_STRING_TO_NUMBER_H_