C++ 将 System::String 转换为 Const Char *
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Converting System::String to Const Char *
提问by Reznor
I am using Visual C++ 2008's GUI creator to make a user interface. When a button is clicked, the following function is called. The content is supposed to create a file and name the file after the contents of the textbox "Textbox' with '.txt' at the end. However, that leads me to a conversion error. Here is the code:
我正在使用 Visual C++ 2008 的 GUI 创建器来制作用户界面。单击按钮时，将调用以下函数。内容应该创建一个文件，并在文本框“Textbox”的内容后命名文件，末尾带有“.txt”。但是，这导致我出现转换错误。这是代码：
private: System::Void Button_Click(System::Object^ sender, System::EventArgs^ e) {
ofstream myfile (Textbox->Text + ".txt");
myfile.close();
}
private: System::Void Button_Click(System::Object^ sender, System::EventArgs^ e) {
ofstream myfile (Textbox->Text + ".txt");
myfile.close();
}
Here is the error:
这是错误：
error C2664: 'std::basic_ofstream<_Elem,_Traits>::basic_ofstream(const char *,std::ios_base::openmode,int)' : cannot convert parameter 1 from 'System::String ^' to 'const char *'
错误 C2664：“std::basic_ofstream<_Elem,_Traits>::basic_ofstream(const char *,std::ios_base::openmode,int)”：无法将参数 1 从“System::String ^”转换为“const char *” '
How can I do a conversion to allow this to go through?
我怎样才能进行转换以允许它通过？
回答by Timber Wolf
It's simple!
这很简单！
As you're using managed C++, use the include and operate like:
当您使用托管 C++ 时，请使用包含和操作，如：
#include <msclr/marshal.h>
...
void someFunction(System::String^ oParameter)
{
msclr::interop::marshal_context oMarshalContext;
const char* pParameter = oMarshalContext.marshal_as<const char*>(oParameter);
// the memory pointed to by pParameter will no longer be valid when oMarshalContext goes out of scope
}
回答by jdehaan
I would use marshalling:
我会使用编组：
//using namespace System::Runtime::InteropServices;
const char* str = (const char*)(void*)
Marshal::StringToHGlobalAnsi(Textbox->Text);
// use str here for the ofstream filename
Marshal::FreeHGlobal(str);
But note that you then use just Ansi strings. If you need unicode support you can use the widechar STL class wofstreamand PtrToStringChars(#include <vcclr.h>) to convert from System::String. In that case you do not need to free the pinned pointer.
但请注意，您随后仅使用 Ansi 字符串。如果您需要 unicode 支持，您可以使用宽字符 STL 类wofstream和PtrToStringChars( #include <vcclr.h>) 从System::String. 在这种情况下，您不需要释放固定指针。
回答by Sergey Teplyakov
#include <string>
#include <iostream>
#include <atlbase.h>
#include <atlconv.h>
#include <vcclr.h>
using namespace System;
int main(array<System::String ^> ^args)
{
String^ managedStr = gcnew String(L"Hello, Managed string!");
//If you want to convert to wide string
pin_ptr<const wchar_t> wch = PtrToStringChars(managedStr);
std::wstring nativeWstr(wch);
//if you want to convert to std::string without manual resource cleaning
std::string nativeStr(CW2A(nativeWstr.c_str()));
std::cout<<nativeStr<<std::endl;
Console::WriteLine(L"Hello World");
return 0;
}
回答by danger89
Thanks jdehaan. I little modified the code to use it with my 'normal' System::String's.
谢谢杰德汉。我几乎没有修改代码以将它与我的“正常” System::String 一起使用。
void MarshalNetToStdString(System::String^ s, std::string& os)
{
using System::IntPtr;
using System::Runtime::InteropServices::Marshal;
const char* chars = (const char*)(Marshal::StringToHGlobalAnsi(s)).ToPointer( );
os = chars;
Marshal::FreeHGlobal(IntPtr((void*)chars));
}
This is the way if you want to convert System:String -> std:string.
如果您想转换 System:String -> std:string，这就是方法。
回答by Meister Schnitzel
There is an really excellent article in MSDN about String conversions here:
MSDN 中有一篇关于字符串转换的非常出色的文章：
http://msdn.microsoft.com/en-us/library/ms235631%28vs.80%29.aspx
http://msdn.microsoft.com/en-us/library/ms235631%28vs.80%29.aspx
There are many samples to convert String from and to different types.
有许多示例可以将 String 从不同类型转换为不同类型。
回答by Ruddy
You can convert it to a CString and then add the extension to it.
您可以将其转换为 CString，然后向其中添加扩展名。
There is a built-in CString constructor which will allow this conversion to happen
有一个内置的 CString 构造函数，它将允许这种转换发生
Example:
例子：
CString(Textbox->Text)
In your specific case:
在您的具体情况下：
private: System::Void Button_Click(System::Object^ sender, System::EventArgs^ e)
{
ofstream myfile (CString(Textbox->Text) + ".txt");
myfile.close();
}
