Error when passing a 'system::string' to a function - c++

Question

I have the following function, which will hopefully tell me whether or not a folder exists, but when I call it, I get this error -
cannot convert parameter 1 from 'System::String ^' to 'std::string'
The function -
#include <sys/stat.h>
#include <string>
bool directory_exists(std::string path){
struct stat fileinfo;
return !stat(path.c_str(), &fileinfo);
}
The call (from the form.h file that holds the form where the user selects the folder) -
private:
System::Void radioListFiles_CheckedChanged(System::Object^ sender, System::EventArgs^ e) {
if(directory_exists(txtActionFolder->Text)){
this->btnFinish->Enabled = true;
}
}
Is anyone able to tell me how to filx this? Thanks.

Answer 1

You're trying to convert from a managed, C++/CLI string (System::String^) into a std::string. There is no implicit conversion provided for this.
In order for this to work, you'll have to handle the string conversion yourself.
This will likely look something like:
std::string path = context->marshal_as<std::string>(txtActionFolder->Text));
if(directory_exists(path)) {
this->btnFinish->Enabled = true;
}
That being said, in this case, it might be easier to stick to managed APIs entirely:
if(System::IO::Directory::Exists(txtActionFolder->Text)) {
this->btnFinish->Enabled = true;
}

Answer 2

You are trying to convert a CLR string to a STL string to convert it to a C-string to use it with a POSIX-emulation function. Why such a complication? Since you are using C++/CLI anyway, just use System::IO::Directory::Exists.

Answer 3

To make this work you need to convert from the managed type System::String to the native type std::string. This involves a bit of marshaling and will result in 2 separate string instances. MSDN has a handy table for all of the different types of marshaling for strings
http://msdn.microsoft.com/en-us/library/bb384865.aspx
In this particular case you can do the following
std::string nativeStr = msclr::interop::marshal_as<std::string>(managedStr);