Allow changing the format of StringMaker<float> and StringMaker<double>

docs/tostring.md

@@ -127,6 +127,17 @@ inside the `StringMaker` specialization, like so:
 This assertion will fail and print out the `testFloat1` and `testFloat2`
 to 15 decimal places.
 
+`StringMaker<float>` and `StringMaker<double>` default to using fixed output,
+but can be set to use scientific notation by modifying the `format` static
+variable:
+
+```cpp
+        Catch::StringMaker<float>::format = std::scientific;
+        const float testFloat1 = 1e-5f;
+        const float testFloat2 = 1e-6f;
+        REQUIRE(testFloat1 == testFloat2);
+```
+
 ---
 
 [Home](Readme.md#top)

src/catch2/catch_tostring.cpp

@@ -42,14 +42,14 @@ namespace Detail {
         };
 
         template<typename T>
-        std::string fpToString(T value, int precision) {
+        std::string fpToString(T value, int precision, std::ios_base &(*format)(std::ios_base &)) {
             if (Catch::isnan(value)) {
                 return "nan";
             }
 
             ReusableStringStream rss;
             rss << std::setprecision(precision)
-                << std::fixed
+                << format
                 << value;
             std::string d = rss.str();
             std::size_t i = d.find_last_not_of('0');
@@ -225,15 +225,17 @@ std::string StringMaker<unsigned char>::convert(unsigned char c) {
 }
 
 int StringMaker<float>::precision = 5;
+std::ios_base &(*StringMaker<float>::format)(std::ios_base &) = std::fixed;
 
 std::string StringMaker<float>::convert(float value) {
-    return Detail::fpToString(value, precision) + 'f';
+    return Detail::fpToString(value, precision, format) + 'f';
 }
 
 int StringMaker<double>::precision = 10;
+std::ios_base &(*StringMaker<double>::format)(std::ios_base &) = std::fixed;
 
 std::string StringMaker<double>::convert(double value) {
-    return Detail::fpToString(value, precision);
+    return Detail::fpToString(value, precision, format);
 }
 
 } // end namespace Catch
@@ -241,4 +243,3 @@ std::string StringMaker<double>::convert(double value) {
 #if defined(__clang__)
 #    pragma clang diagnostic pop
 #endif
-

src/catch2/catch_tostring.hpp

@@ -271,12 +271,14 @@ namespace Catch {
     struct StringMaker<float> {
         static std::string convert(float value);
         static int precision;
+        static std::ios_base &(*format)(std::ios_base &);
     };
 
     template<>
     struct StringMaker<double> {
         static std::string convert(double value);
         static int precision;
+        static std::ios_base &(*format)(std::ios_base &);
     };
 
     template <typename T>