running code doesn't work when being used in dll - c++

Question

I'm programming in c++ in Visual Studio.
This is my subroutine, which gives me a specific value back from a double array:
double specific_value_search(std::string mol_fractions_name[], std::string mass_fractions_name_output[], double mass_fractions_output[], int molecule)
{
double specific_value=5;
std::string a = mol_fractions_name[molecule];
std::string b;
for (int i = 0; i <= 11; i++)
{
b = mass_fractions_name_output[i];
if (a.compare(b) == 0)
//if ((a.find(b) != std::string::npos))...this was my second try // sollte string b in Zeile a gefunden werden, dann...
{
specific_value = mass_fractions_output[i];
break;
}
}
return specific_value;
}
so when I execute this code in my project to an .exe, the code runs fine.
but when I compile it to an dll, an run it via an external program, the value returns 5, because of my initalisation (without initialisation the program crashes because of trying to return an uninitialized variable.
I added the values from visual studio in the screenshots below
Does anyone have any advice?
Screenshot 1 - values from visual studio
Screenshot 2 - values from visual studio

Answer 1

If you can use a standard container (std::map or std::unsorted_map) then this becomes trivial.
std::map<std::string, double> fractionNames;
// fill map
double specificValue = fractionNames[mol_fractions_name[molecule]];
If it's possible that molecule is bigger than the number of names or that you need to generate an error if the fraction name isn't found in the map then you'll have to add some code to detect and handle these situations.
If you can't use a map, then you could use a vector
struct FractionName {
std::string name;
double value;
}
typedef std::vector<FractionName> FractionNameVector;
FractionNameVector fractionNames;
// again fill fractionNames
FractionNameVector::iterator iter = std::find(fractionNames.begin(), fractionNames.end(), SearchPredicate(mol_fractions_name[molecule]));
This will need a SearchPredicate like this
struct SearchPredicate
{
bool operator()(const FractionName& haystack) { return haystack.name ==
needle; }
explicit SearchPredicate(const std::string name) : needle(name) {}
std::string needle;
};
You could use a lambda if you are using C++11 or later.