How can I convert a 'System::String ^' to 'const char *' in vc++?
My code:
String ^Result1= "C:/Users/Dev/Desktop/imag.jpg";
IplImage *img1 = cvLoadImage(Result1, 1);
if I do like above it will generate following error.
error C2664: 'cvLoadImage' : cannot convert parameter 1 from 'System::String ^' to 'const char *'
Please help me.
It's like this: How to convert from System::String* to Char* in Visual C++
System::String ^ str = "Hello world\n";
//method 1
pin_ptr<const wchar_t> str1 = PtrToStringChars(str);
wprintf(str1);
//method 2
char* str2 = (char*)Marshal::StringToHGlobalAnsi(str).ToPointer();
printf(str2);
Marshal::FreeHGlobal((IntPtr)str2);
//method 3
CString str3(str);
wprintf(str3);
//method 4
#if _MSC_VER > 1499 // Visual C++ 2008 only
marshal_context ^ context = gcnew marshal_context();
const char* str4 = context->marshal_as<const char*>(str);
puts(str4);
delete context;
#endif
This is work for me.
void MarshalString ( String ^ s, string& os ) {
using namespace Runtime::InteropServices;
const char* chars =
(const char*)(Marshal::StringToHGlobalAnsi(s)).ToPointer();
os = chars;
Marshal::FreeHGlobal(IntPtr((void*)chars));
}
Related
I have code:
char buff[50000];
CString params = "sss" ;
strcpy_s(buff,params);
Why strcpy_s accepts second param that is CString? According to my understanding second param should be of type const char * _Source
CString has a LPCTSTR conversion operator. The compiler calls this to convert your CString to the required const char *. So what the compiler does is:
strcpy_s(buff, (const char*)params);
which is equivalent to
strcpy_s(buff, (LPCTSTR)params);
which is like
strcpy_s(buff, params.operator LPCTSTR());
This only works if you are not compiling for Unicode. On Unicode LPCTSTR is not const char * but const WCHAR *, so this would not work.
I programmed a little Application in C++. There is a ListBox in the UI. And I want to use the selected Item of ListBox for an Algorithm where I can use only wstrings.
All in all I have two questions:
-how can I convert my
String^ curItem = listBox2->SelectedItem->ToString();
to a wstring test?
-What means the ^ in the code?
Thanks a lot!
It should be as simple as:
std::wstring result = msclr::interop::marshal_as<std::wstring>(curItem);
You'll also need header files to make that work:
#include <msclr\marshal.h>
#include <msclr\marshal_cppstd.h>
What this marshal_as specialization looks like inside, for the curious:
#include <vcclr.h>
pin_ptr<WCHAR> content = PtrToStringChars(curItem);
std::wstring result(content, curItem->Length);
This works because System::String is stored as wide characters internally. If you wanted a std::string, you'd have to perform Unicode conversion with e.g. WideCharToMultiByte. Convenient that marshal_as handles all the details for you.
I flagged this as a duplicate, but here's the answer on how to get from System.String^ to a std::string.
String^ test = L"I am a .Net string of type System::String";
IntPtr ptrToNativeString = Marshal::StringToHGlobalAnsi(test);
char* nativeString = static_cast<char*>(ptrToNativeString.ToPointer());
The trick is make sure you use Interop and marshalling, because you have to cross the boundary from managed code to non-managed code.
My version is:
Platform::String^ str = L"my text";
std::wstring wstring = str->Data();
With Visual Studio 2015, just do this:
String^ s = "Bonjour!";
C++/CLI
#include <vcclr.h>
pin_ptr<const wchar_t> ptr = PtrToStringChars(s);
C++/CX
const wchart_t* ptr = s->Data();
According to microsoft:
Ref How to: Convert System::String to Standard String
You can convert a String to std::string or std::wstring, without using PtrToStringChars in Vcclr.h.
// convert_system_string.cpp
// compile with: /clr
#include <string>
#include <iostream>
using namespace std;
using namespace System;
void MarshalString ( String ^ s, string& os ) {
using namespace Runtime::InteropServices;
const char* chars =
(const char*)(Marshal::StringToHGlobalAnsi(s)).ToPointer();
os = chars;
Marshal::FreeHGlobal(IntPtr((void*)chars));
}
void MarshalString ( String ^ s, wstring& os ) {
using namespace Runtime::InteropServices;
const wchar_t* chars =
(const wchar_t*)(Marshal::StringToHGlobalUni(s)).ToPointer();
os = chars;
Marshal::FreeHGlobal(IntPtr((void*)chars));
}
int main() {
string a = "test";
wstring b = L"test2";
String ^ c = gcnew String("abcd");
cout << a << endl;
MarshalString(c, a);
c = "efgh";
MarshalString(c, b);
cout << a << endl;
wcout << b << endl;
}
output:
test
abcd
efgh
I want to initialize bits of a variable of unsigned char with a string of binary digits, but I don't know how to do it.
From your comments, it seems like you want to parse an ASCII string of binary digits. This is how you do that:
#include <stdlib.h>
const char* binary = "10001001";
char* next;
unsigned char value = strtoul(binary, &next, 2);
if (*next) { /* conversion failed */ }
unsigned char s[] = "How now brown cow.\n";
For this line of code:
int currentSnapshotHeight = _wtoi(ExecuteExternalProgram(L"current.png"));
I got this error:
Error 1 error C2664: '_wtoi' : cannot convert parameter 1 from 'ATL::CString' to 'const wchar_t *'
How to fix?
Maybe this will work?
int currentSnapshotHeight = _wtoi(ExecuteExternalProgram(_T("current.png")));
Also check if Unicode setting of project are set as expected.
Try this:
int currentSnapshotHeight = _wtoi((wchar_t*)ExecuteExternalProgram(L"current.png").GetBuffer());
When I compile this code in Visual C++, I got the below error. Can help me solve this issue..
DWORD nBufferLength = MAX_PATH;
char szCurrentDirectory[MAX_PATH + 1];
GetCurrentDirectory(nBufferLength, szCurrentDirectory);
szCurrentDirectory[MAX_PATH +1 ] = '\0';
Error message:
Error 5 error C2664: 'GetCurrentDirectoryW' : cannot convert parameter 2 from 'char [261]' to 'LPWSTR' c:\car.cpp
Your program is configured to be compiled as unicode. Thats why GetCurrentDirectory is GetCurrentDirectoryW, which expects a LPWSTR (wchar_t*).
GetCurrentDirectoryW expects a wchar_t instead of char array. You can do this using TCHAR, which - like GetCurrentDirectory - depends on the unicode setting and always represents the appropriate character type.
Don't forget to prepend your '\0' with an L in order to make the char literal unicode, too!
It seems you have define UNICODE, _UNICODE compiler flags. In that case, you need to change the type of szCurrentDirectory from char to TCHAR.
Headers:
#include <iostream>
#include <fstream>
#include <direct.h>
#include <string.h>
#include <windows.h> //not sure
Function to get current directory:
std::string getCurrentDirectoryOnWindows()
{
const unsigned long maxDir = 260;
wchar_t currentDir[maxDir];
GetCurrentDirectory(maxDir, currentDir);
std::wstring ws(currentDir);
std::string current_dir(ws.begin(), ws.end());
return std::string(current_dir);
}
To call function:
std::string path = getCurrentDirectoryOnWindows(); //Output like: C:\Users\NameUser\Documents\Programming\MFC Program 5
To make dir (Folder) in current directory:
std::string FolderName = "NewFolder";
std::string Dir1 = getCurrentDirectoryOnWindows() + "\\" + FolderName;
_mkdir(Dir1.c_str());
This works for me in MFC C++.