Fix C API getMeterHandle() to Return a Valid Handle for the First Meter

src/EnergyPlus/OutputProcessor.cc

@@ -4102,8 +4102,8 @@ int GetMeterIndex(EnergyPlusData const &state, std::string const &name)
     //       DATE WRITTEN   August 2002
 
     // PURPOSE OF THIS FUNCTION:
-    // This function returns a index to the meter "number" (aka assigned report number)
-    // for the meter name.  If none active for this run, a zero is returned.  This is used later to
+    // This function returns an index to the meter "number" (aka assigned report number)
+    // for the meter name. If none is active for this run, -1 is returned. This is used later to
     // obtain a meter "value".
 
     auto const &op = state.dataOutputProcessor;

src/EnergyPlus/api/datatransfer.cc

@@ -386,12 +386,7 @@ int getMeterHandle(EnergyPlusState state, const char *meterName)
 {
     auto *thisState = static_cast<EnergyPlus::EnergyPlusData *>(state);
     std::string const meterNameUC = EnergyPlus::Util::makeUPPER(meterName);
-    const int i = EnergyPlus::GetMeterIndex(*thisState, meterNameUC);
-    if (i == 0) {
-        // inside E+, zero is meaningful, but through the API, I want to use negative one as a signal of a bad lookup
-        return -1;
-    }
-    return i;
+    return EnergyPlus::GetMeterIndex(*thisState, meterNameUC);
 }
 
 Real64 getMeterValue(EnergyPlusState state, int handle)

tst/EnergyPlus/unit/OutputProcessor.unit.cc

@@ -47,6 +47,8 @@
 
 // EnergyPlus::OutputProcessor Unit Tests
 
+#include <algorithm>
+
 // Google Test Headers
 #include <gtest/gtest.h>
 
@@ -67,6 +69,7 @@
 #include <EnergyPlus/ScheduleManager.hh>
 #include <EnergyPlus/SystemReports.hh>
 #include <EnergyPlus/WeatherManager.hh>
+#include <EnergyPlus/api/datatransfer.h>
 
 #include <climits>
 #include <map>
@@ -5313,6 +5316,11 @@ namespace OutputProcessor {
         EXPECT_EQ(1, op->EndUseCategory(2).NumSubcategories);
         EXPECT_EQ("General", op->EndUseCategory(2).SubcategoryName(1));
 
+        auto const zeroMeter = std::find_if(op->meterMap.begin(), op->meterMap.end(), [](auto const &meterEntry) { return meterEntry.second == 0; });
+        ASSERT_NE(op->meterMap.end(), zeroMeter);
+        EXPECT_EQ(0, getMeterHandle(state, zeroMeter->first.c_str()));
+        EXPECT_EQ(GetMeterIndex(*state, "ELECTRICITY:FACILITY"), getMeterHandle(state, "Electricity:Facility"));
+
         int found = GetMeterIndex(*state, "COOLING:ELECTRICITY");
         EXPECT_NE(-1, found);
         EXPECT_EQ((int)Constant::eResource::Electricity, (int)op->meters[found]->resource);