Refactor static variables in OpenSim::IO

CHANGELOG.md

@@ -41,6 +41,7 @@ v4.6
   states belong, a date/time stamp of when the file was written, and a user-specified note. `.ostate` files also support a
   configurable output precision. At the highest ouput precsion (~20 significant figures), serialization/deserialization is
   a lossless process. (#3902)
+- Improved `OpenSim::IO::stod` string-to-decimal parsing function by making it not-locale-dependant (#3943, #3924; thanks @alexbeattie42)
 
 v4.5.1
 ======

OpenSim/Common/IO.cpp

@@ -60,13 +60,28 @@ using namespace OpenSim;
 using namespace std;
 
 // STATICS
-bool IO::_Scientific = false;
-bool IO::_GFormatForDoubleOutput = false;
-int IO::_Pad = 8;
-int IO::_Precision = 8;
-char IO::_DoubleFormat[] = "%16.8lf";
-bool IO::_PrintOfflineDocuments = true;
-const std::locale _locale = std::locale::classic(); 
+namespace
+{
+    constexpr int IO_DBLFMTLEN = 256;
+
+    /** Specifies whether number output is in scientific or float format. */
+    bool _Scientific = false;
+
+    /** Specifies whether number output is in %g format or not. */
+    bool _GFormatForDoubleOutput = false;
+
+    /** Specifies number of digits of padding in number output. */
+    int _Pad = 8;
+
+    /** Specifies the precision of number output. */
+    int _Precision = 8;
+
+    /** The output format string. */
+    char _DoubleFormat[IO_DBLFMTLEN] = "%16.8lf";
+
+    /** Whether offline documents should also be printed when Object::print is called. */
+    bool _PrintOfflineDocuments = true;
+}
 
 
 //=============================================================================
@@ -482,10 +497,16 @@ double IO::
 stod(const std::string& __str, std::size_t* __idx)
 { 
     std::istringstream iss(__str);
-    iss.imbue(_locale);
+
+    // Always parse numbers with "C" locale, which uses a period character
+    // for the decimal place. Otherwise, Finns, Dutch, and other locales
+    // that use comma characters as a decimal place will encounter parsing
+    // issues (#3943, #3924).
+    iss.imbue(std::locale::classic());
+
     double result;
     iss >> result;
-    if(iss.fail()){
+    if (iss.fail()) {
         result = std::numeric_limits<double>::quiet_NaN();
         log_warn("Encountered non-numeric string value: {} ; parsed value:{}",__str, result);
     }

OpenSim/Common/IO.h

@@ -35,7 +35,6 @@
 
 // DEFINES
 constexpr int IO_STRLEN = 2048;
-constexpr int IO_DBLFMTLEN = 256;
 
 
 namespace OpenSim { 
@@ -53,19 +52,6 @@ class OSIMCOMMON_API IO {
 // DATA
 //=============================================================================
 private:
-    // NUMBER OUTPUT
-    /** Specifies whether number output is in scientific or float format. */
-    static bool _Scientific;
-    /** Specifies whether number output is in %g format or not. */
-    static bool _GFormatForDoubleOutput;
-    /** Specifies number of digits of padding in number output. */ 
-    static int _Pad;
-    /** Specifies the precision of number output. */
-    static int _Precision;
-    /** The output format string. */
-    static char _DoubleFormat[IO_DBLFMTLEN];
-    /** Whether offline documents should also be printed when Object::print is called. */
-    static bool _PrintOfflineDocuments;
 
 
 //=============================================================================