I was reading the c++'s foreach syntax on MSDN:
// for_each_string1.cpp
// compile with: /ZW
#include <stdio.h>
using namespace Platform;
ref struct MyClass {
property String^ MyStringProperty;
};
int main() {
String^ MyString = ref new String("abcd");
for each ( char c in MyString )
wprintf("%c", c);
wprintf("/n");
MyClass^ x = ref new MyClass();
x->MyStringProperty = "Testing";
for each( char c in x->MyStringProperty )
wprintf("%c", c);
}
I tried to find what the "^" means on google but I couldn't find anything (or my query wasn't correct)
What does it mean? Is it as a "*"? Is it as a "&"?
This syntax also applies to C#. Do they mean the same thing in both languages?
Piece of C# code:
using namespace System;
int main(){
array<int>^ arr = gcnew array<int>{0,1,2,5,7,8,11};
int even=0, odd=0;
for each (int i in arr) {
if (i%2 == 0)
even++;
else
odd++;
}
Console::WriteLine(“Found {0} Odd Numbers, and {1} Even Numbers.”,
odd, even);
}
The "^" denotes a managed reference, which is used for managed types. It's like a pointer, but for managed types. The syntax doesn't exist in C#. In C#, the equivalent is just a variable of a reference type (as opposed to a value type), or a boxed value type.
As others have said, this is C++/CLI syntax which means you have to compile with the /clr option. C++/CLI is basically C++ with features of C# (or more generally, .NET).
https://learn.microsoft.com/en-us/cpp/extensions/handle-to-object-operator-hat-cpp-component-extensions?view=vs-2019 hope this link can help you.
btw,^ is a special character and ignored by google search engine so you can not search that.
Related
Let's have a look at this little application:
#include <QString>
#include <QDebug>
int main(int argc, char *argv[]) {
const auto test_string =
QString{"Some string \n \x01 \u0002 with some \r special chars"};
qDebug() << test_string;
qDebug(qPrintable(test_string));
}
It gives the following output:
"Some string \n \u0001 \u0002 with some \r special chars"
Some string
special chars
Press <RETURN> to close this window...
This demonstrates how the qDebug << operator comes with some functionality that converts all the special characters of a QString to some readable string, which can easily be put in a string declaration in C++.
I would like to use this functionality to feed strings into a custom logging framework. Is there a possibility to use the same conversion function directly?
Effectively, this would mean to convert test_string to a QString instance that gives the same output on both the above qDebug statements.
I had the same question and I did not found the complete answer (yet). However, I found QVariant which allows you to call toString() on the most basic C and Qt types:
QVariant("foo").toString(); // "foo"
QVariant(true).toString(); // "true"
QVariant(QDateTime("2020-11-28")).toString(); // "2020-11-28"
Then you could wrap this into one method:
QString variantToString(const QVariant variant) {
return (variant.userType() != QMetaType::QString
&& variant.canConvert(QMetaType::QStringList))
? "(" + variant.toStringList().join(", ") + ")"
: variant.toString();
}
variantToString(42); // "42" // works due to implicit cast
You could do a few extra checks for non-stringifiable types (see also canConvert() and userType(), e.g. lists, regular expressions or whatever you need, but I totally agree that it would be nicer to reuse Qt's own logging functions instead ...
I had a similar issue but I wanted to use my custom operator<< overload that was defined for QDebug, therefore, I did the following:
// This could be anything that provides an 'operator<<' overload.
QString value = "Hello, world!";
QString result;
QDebug{ &result } << value;
I am receiving a dictionary from a C# dll to C++/CLI code. I am trying to convert dictionary into std::map which will be further used by old C++ code. but I am not able to do. I have a function which is will take dictionary as parameter and return a map.
This is what I am trying to do-
std::map < std::wstring, std::map<int, int>> Convert(Dictionary<String^, Dictionary<int, int>^>^ myMap)
{
std::map < std::wstring, std::map<int, int>> h_result;
for (std::wstring& stringKey : myMap->Keys)
{
for (std::pair<int, int> intKey : (myMap->Values))
{
h_result.insert(stringKey, intKey);
}
}
return h_result;
}
I am getting error while iterating the values.
error:this range-based 'for' statement requires a suitable "begin" function and none was found
Can anybody tell what is the problem here? or if there is any better way to convert Dictionary^ into std::map, please do suggest me.
I am new with dictionary and std::map. please let me know if there is any silly mistake with the sample code.
You're (a) trying to use C++ range-for loops with Dictionary^, and (b) trying to use System types interchangeably with C++ standard types. All of which won't work.
You need to do this a bit more step-by-step: iterate the Dictionary^ collections with for each, convert the String^ to std::wstring properly, and create the map items with std::make_pair.
So your function will look something like this (untested)
std::map <std::wstring, std::map<int, int>> Convert(Dictionary<String ^, Dictionary<int, int>^> ^myMap)
{
std::map <std::wstring, std::map<int, int>> h_result;
// iterate the outer dictionary
for each(KeyValuePair<String ^, Dictionary<int, int>^> ^kvp1 in myMap)
{
std::wstring stringKey = marshal_as<std::wstring>(kvp1->Key);
std::map<int, int> mapValues;
// iterate the inner dictionary
for each(KeyValuePair<int, int> ^kvp2 in kvp1->Value)
{
// insert in inner map
mapValues.insert(std::make_pair(kvp2->Key, kvp2->Value));
}
// insert in outer map
h_result.insert(std::make_pair(stringKey, mapValues));
}
return h_result;
}
I've got the following struct:
struct Param
{
double** K_RP;
};
And I wanna perform the following operations on "K_RP" in CUDA
__global__ void Test( struct Param prop)
{
int ix = threadIdx.x;
int iy = threadIdx.y;
prop.K_RP[ix][iy]=2.0;
}
If "prop" has the following form, how should I do my "cudaMalloc" and "cudaMemcpy" operations?
int main( )
{
Param prop;
Param cuda_prop;
prop.K_RP=alloc2D(Imax,Jmax);
//cudaMalloc cuda_prop ?
//cudaMemcpyH2D prop to cuda_prop ?
Test<<< (1,1), (Imax,Jmax)>>> ( cuda_prop);
//cudaMemcpyD2H cuda_prop to prop ?
return (0);
}
Questions like this get asked from time to time. If you search on the cuda tag, you'll find a variety of examples with answers. Here's one example.
In general, dynamically allocated data contained within structures or other objects requires special handling. This question/answer explains why and how to do it for the single pointer (*) case.
Handling double pointers (**) is difficult enough that most people would recommend "flattening" the storage so that it can be handled by reference with a single pointer (*). If you really want to see how the double pointer (**) method works, review this question/answer. It's not trivial.
Using Qt, I want this code to work:
QList<QPair<QString, QString>> list;
foreach (QPair<QString, QString> pair, list)
{
}
instead, I get the error:
'pair' : undeclared identifier
Using a typedef I can make it work, but this is not what I want (unless this is the only thing that works):
typedef QPair<QString, QString> MyPair;
QList<MyPair> list;
foreach (MyPair pair, list)
{
}
Can anyone explain why the first foreach doesn't compile?
it's not the foreach error. It's declaration error. You declared list like this:
QList<QPair<QString, QString>> list;
while it should this way:
QList<QPair<QString, QString> > list;
Just declare QPair outside of loop:
QPair<QString,QString> pair;
foreach(pair,list){
}
It is not possible to use template classes inside qt foreach statement which contains more than one template parameter, because comma separator conflicts with comma separator inside macros.
#define add( a, b ) (a + b)
template < typename T1, typename T2 >
struct DATA
{
static const T1 val1 = 1;
static const T2 val2 = 2;
};
// Usage
const int c = add( 1, 2 ); // OK
const int d = add( DATA< int, int >::val1 , DATA< int, int >::val2 ); // FAIL
because macros add will interpret "DATA< int" as first argument, and " int >::val1" as second, and so on.
Some explanation with above answer... if your compiler accept
QList<QPair<QString, QString>> list;
giving no error on such declaration, reasons for topic caster error is different and indeed has to do with a fact that declaration must be done outside of foreach() loop. That's explained in QT documentation.
regarding >> and > >... that's old story and latest GCC (so linux/mac) consider it to be a syntax mistake, because it's not conforming standard. >> in GCC manner is treated as operator with all follow-up errors..
I dont know a lot about C++, but I have to make work some C++ code with .NET. I try with DLLImport but I failed. So I try with C++/CLI to make kind of a wrapper.
But I'm not sure to understand everything...
This is the basic C++ H file with the function I want to export (MyFunction)
extern "C"
{
__declspec(dllexport) IplImage* MyFunction(IplImage *src, std::string* name, OneEnumerationType myEnum, bool myBool, float myFloat);
}
This is the Wrapper h code.
#include "MyFunction.h"; // the file containing the h code
#include <string>
namespace MyWrapper{
public ref class MyWrapperClass {
public:
MyWrapper(){};
IplImage^ GetMyFunction(IplImage *src, std::string^ name, OneEnumerationType myEnum, bool myBool, float myFloat);
}
This is the Wrapper cpp code.
#include "MyWrapperCode.h";
namespace MyWrapper{
IplImage^ MyWrapperClass::GetMyFunction(IplImage* src, std:string^ name, OneEnumerationType myEnum, bool myBool, float myFloat){
MyFunction(src, name, myEnum, myBool, myFloat);
}
}
These are my questions :
1) When I'm compiling, the error is "'^ : cannot use this indirection on type IplImage' and same message for type "std::string".
I have followed this logical :
ClasseNative clNat2 = *clNat; --> ClasseManagee clMan2 = *clMan;
ClasseNative &clNat3 = clNat2; --> ClasseManagee %clMan3 = clMan2;
ClasseNative *clNat4 = &clNat2; --> ClasseManagee ^clMan4 = %clMan2;
I have seen, that It was better to use System::String. I try this way but the initial function is using std::string... BTW, why is it better to change ?
2) How do I get the MyFunction IplImage result ? Thru a private member and a get I suppose but I dont know how to initialize it...
3) Tricky question. Is it possible for me to put the CLI obtains IplImage structure (from the OpenCV library) (the result of my function) inside a IplImage .NET structure, when I ll called my wrapper ? Dont know if the question is understandable...
Thanks a lot for your help.
Turning around for 3 days on this problem...
Your wrapper class needs to create a new std::string based on the content of a System::String^ parameter then pass to your native function. Otherwise you need to rewrite the function to take something else as the string input, for example a LPWSTR or LPCSTR.
You can write a ref class to have properties for all data that an IplImage would have, then pass that to your wrapper class. Your wrapper class then create an IplImage object based on the data of the ref class and pass to the native function. Reverse the data copying direction for the return value.
1) just by adding ^ you cannot change a native object to become managed, you have to create wrappers or transfer the data for example:
std::string nativeString = "my string";
String^ managedString = gcnew String(nativeString.c_str());
//now you can return it as
2) create a managed wrapper or use primitive datatype to transfer the data
3) note sure if this will help but look at Emgu.CV
try reading abit more about C++\CLI here are a few nice tutorials:
Quick C++/CLI - Learn C++/CLI in less than 10 minutes
C++/CLI for the C# programmer