C++/CLI Converting System::String to const char*

Question

I'm using Microsoft Visual C++ 2008 I want to join some strings, and then use it with "system" command.

I tried to do it like this:

System::String^ link;
link = "wget.exe --output-document=log http://ADDRESS";
link = link + System::String::Copy(textBox_login->Text);
link = link + "&passwd=";
link = link + System::String::Copy(textBox_passwd->Text);
system(link); //LINE WITH ERROR

But i get error C2664: 'system' : cannot convert parameter 1 from 'System::String ^' to 'const char *'

I appreciate any help ;)

Answer 1

Take a look at this question and this question.

In essence, the problem is that the system function expects a variable of the type const char* rather than System::String.

So you need to convert the string to a const char* (Using code from this answer) and use that as an argument for the system function.

IntPtr p = Marshal::StringToHGlobalAnsi(clistr);
const char* linkStr = static_cast<char*>(p.ToPointer());
system(linkStr);
Marshal::FreeHGlobal(p);

Answer 2

To use system as you do, you will need Marshalling. This requires extra precautions which can lead to unforeseen pain.

I recommend that you call wget via the System::Process class

It integrates with .NET much better and you can use System::String^ directly

Answer 3

after doing as Yacoby said, almost everything works fine, but when it gets to

link = link + "&passwd=";

it cuts everything what is afterwords in string. when i remove '&' it works just fine... i need the '&' sign

Answer 4

You got the technical solution to your problem but here are a couple other things you might want to consider:

• Instead of opening a process to do the HTTP request for you, use an API (.NET or C++, in .NET it's much easier than standard C++, look at WebRequest) to do this. Especially if you plan to do something with the response.

• In general if you're appending to a String multiple times, prefer a StringBuilder. Since String is immutable in .NET, every append requires a new String to be constructed.

• In this case, don't use a String to build the URL in the first place. Use System::Uri instead.