Merge bitcoin/bitcoin#20457: util: Make Parse{Int,UInt}{32,64} use locale independent std::from_chars(…) (C++17) instead of locale dependent strto{l,ll,ul,ull}

4747db876154ddd828c03d9eda10ecf8b25d8dc8 util: Introduce ToIntegral<T>(const std::string&) for locale independent parsing using std::from_chars(…) (C++17) (practicalswift)

Pull request description:

  Make `Parse{Int,UInt}{32,64}` use locale independent `std::from_chars(…)` (C++17) instead of locale dependent `strto{l,ll,ul,ull}`.

  [About `std::from_chars`](https://en.cppreference.com/w/cpp/utility/from_chars): _"Unlike other parsing functions in C++ and C libraries, `std::from_chars` is locale-independent, non-allocating, and non-throwing."_

ACKs for top commit:
  laanwj:
    Code review ACK 4747db876154ddd828c03d9eda10ecf8b25d8dc8

Tree-SHA512: 40f2cd582bc19ddcf2c498eca3379167619eff6aa047bbac2f73b8fd8ecaefe5947c66700a189f83848751f9f8c05645e83afd4a44a1679062aee5440dba880a

1 files changed, 20 insertions, 0 deletions

diff --git a/src/util/strencodings.h b/src/util/strencodings.h
index 26dc0a0ce3..1217572c45 100644
--- a/src/util/strencodings.h
+++ b/src/util/strencodings.h
@@ -12,8 +12,10 @@
 #include <attributes.h>
 #include <span.h>
 
+#include <charconv>
 #include <cstdint>
 #include <iterator>
+#include <optional>
 #include <string>
 #include <vector>
 
@@ -95,6 +97,24 @@ constexpr inline bool IsSpace(char c) noexcept {
 }
 
 /**
+ * Convert string to integral type T.
+ *
+ * @returns std::nullopt if the entire string could not be parsed, or if the
+ *   parsed value is not in the range representable by the type T.
+ */
+template <typename T>
+std::optional<T> ToIntegral(const std::string& str)
+{
+    static_assert(std::is_integral<T>::value);
+    T result;
+    const auto [first_nonmatching, error_condition] = std::from_chars(str.data(), str.data() + str.size(), result);
+    if (first_nonmatching != str.data() + str.size() || error_condition != std::errc{}) {
+        return std::nullopt;
+    }
+    return {result};
+}
+
+/**
  * Convert string to signed 32-bit integer with strict parse error feedback.
  * @returns true if the entire string could be parsed as valid integer,
  *   false if not the entire string could be parsed or when overflow or underflow occurred.