CODEWITHSUNDEEP
c#c++interoptype-conversion
MoonKnight
MoonKnight

Reputation: 23831

Conversion of const char** to std::vector<std::string>

I have the following wrapper to expose my C++ code to C#

extern "C" {
   LIBRARY_API void GenerateTables(
      const char* version, 
      const char* baseDir, 
      const char** fileList);
} // end extern "C"

void GenerateTables(
   const char* version,
   const char* baseDir,
   const char** fileList)
{
   std::string strVersion(version);
   std::string strBaseDir(baseDir);

   // I now need to convert my const char** to std::vector<std::string> 
   // so it can be passed to another internal method.
}

How can I convert my const char** fileList to std:vector<std::string>. I am relatively new to C++ and there is a clear problem with memory allocation here. I could do something like 

std::vector<std::string> vec;
for (int i = 0; i < fileList.length() /* length() of what!? */; i++)
    vec.push_back(/* what!? */);

How can I do the required conversion and is there a better way of passing in an array of strings (string[]) from C# to C++ via interop?

Thanks for your time.

Upvotes: 1

Views: 1880

Answers (2)

David Heffernan
David Heffernan

Reputation: 613302

You need to give the unmanaged code some way to obtain the length. There are two commonly used approaches:

  1. Pass the length of the array as an extra parameter.
  2. Use a null terminated array. The array ends when you encounter an item that is null.

Either option is simple enough for you to implement. The choice is entirely down to your personal preference.

If you choose the first option then you can populate the vector like this:

std::vector<std::string> files(fileList, fileList + length);

If you choose the second option then you'd use a loop like this:

std::vector<std::string> files;
const char** filePtr = fileList;
while (*filePtr != nullptr)
    files.push_back(*filePtr++);

Upvotes: 4

Ivan
Ivan

Reputation: 2057

You need to know the length of fileList array. Once you know it you can convert fileList using

size_t length = ... ;
std::vector<std::string> files( fileList, fileList + length );

Upvotes: 1

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