Fix the string representation of floating point numbers

src/StringFunctions.cpp

@@ -1,5 +1,6 @@
 #include "StringFunctions.h"
 
+#include <cassert>
 #include <locale>
 
 namespace e57
@@ -14,35 +15,37 @@ namespace e57
       ss << std::scientific << std::setprecision( precision ) << value;
 
       // Try to remove trailing zeroes and decimal point
-      // E.g. 1.23456000000000000e+005  ==> 1.23456e+005
-      // E.g. 2.00000000000000000e+005  ==> 2e+005
+      // e.g. 1.23456000000000000e+005  ==> 1.23456e+005
+      // e.g. 2.00000000000000000e+005  ==> 2e+005
 
       std::string s = ss.str();
-      const size_t len = s.length();
 
       // Split into mantissa and exponent
-      // E.g. 1.23456000000000000e+005  ==> "1.23456000000000000" + "e+005"
-      std::string mantissa = s.substr( 0, len - 5 );
-      std::string exponent = s.substr( len - 5, 5 );
+      // e.g. 1.23456000000000000e+005  ==> "1.23456000000000000" + "e+005"
+      auto index = s.find_last_of( 'e' );
+      assert( index != std::string::npos ); // should not be possible
+
+      std::string mantissa = s.substr( 0, index );
+      const std::string exponent = s.substr( index );
 
       // Double check that we understand the formatting
       if ( exponent[0] == 'e' )
       {
-         // Trim of any trailing zeros in mantissa
-         while ( mantissa[mantissa.length() - 1] == '0' )
+         // Trim trailing zeros from mantissa
+         while ( mantissa.back() == '0' )
          {
-            mantissa = mantissa.substr( 0, mantissa.length() - 1 );
+            mantissa.pop_back();
          }
 
-         // Make one attempt to trim off trailing decimal point
-         if ( mantissa[mantissa.length() - 1] == '.' )
+         // Trim trailing decimal point if possible
+         if ( mantissa.back() == '.' )
          {
-            mantissa = mantissa.substr( 0, mantissa.length() - 1 );
+            mantissa.pop_back();
          }
 
          // Reassemble whole floating point number
          // Check if can drop exponent.
-         if ( exponent == "e+000" )
+         if ( ( exponent == "e+00" ) || ( exponent == "e+000" ) )
          {
             s = mantissa;
          }

test/src/test_StringFunctions.cpp

@@ -11,21 +11,37 @@ TEST( StringFunctions, FloatToStrConversion )
 {
    const auto converted = e57::floatingPointToStr<float>( 3.14159265f, 7 );
 
-   ASSERT_EQ( converted, "3.1415927e+00" );
+   ASSERT_EQ( converted, "3.1415927" );
+}
+
+// https://github.com/asmaloney/libE57Format/issues/147
+TEST( StringFunctions, FloatToStrTrimDecimal )
+{
+   const auto converted = e57::floatingPointToStr<float>( 42.0f, 5 );
+
+   ASSERT_EQ( converted, "4.2e+01" );
+}
+
+// https://github.com/asmaloney/libE57Format/issues/147
+TEST( StringFunctions, FloatToStrTrimExponent )
+{
+   const auto converted = e57::floatingPointToStr<float>( 4.0f, 5 );
+
+   ASSERT_EQ( converted, "4" );
 }
 
 TEST( StringFunctions, DoubleToStrConversion )
 {
    const auto converted = e57::floatingPointToStr<double>( 3.141592653589793238, 17 );
 
-   ASSERT_EQ( converted, "3.14159265358979312e+00" );
+   ASSERT_EQ( converted, "3.14159265358979312" );
 }
 
 TEST( StringFunctions, FloatToStrConversion2 )
 {
    const auto converted = e57::floatingPointToStr<float>( 123456.0f, 7 );
 
-   ASSERT_EQ( converted, "1.2345600e+05" );
+   ASSERT_EQ( converted, "1.23456e+05" );
 }
 
 // Related to https://github.com/asmaloney/libE57Format/issues/172
@@ -45,7 +61,7 @@ TEST( StringFunctions, FloatToStrLocale )
 
    const auto converted = e57::floatingPointToStr<float>( 123456.0f, 7 );
 
-   ASSERT_EQ( converted, "1.2345600e+05" );
+   ASSERT_EQ( converted, "1.23456e+05" );
 
    std::locale::global( std::locale::classic() );
 }