char* to QString: conversion

[abghosh]

Hi

While calling dll file from vb.net I am passing a string value to the qt dllas follows:

<DllImport("G:\Varen_CS\02_Projects\01_Softwares\highFreqTrad\test\debug\test.dll", _
               CharSet:=CharSet.Auto, _
               CallingConvention:=CallingConvention.StdCall)> _
    Private Shared Function _ZN11QtEngineDll7randIntEv(ByRef u As String) As String
    End Function

<DllImport("G:\Varen_CS\02_Projects\01_Softwares\highFreqTrad\test\debug\test.dll", _
               CharSet:=CharSet.Auto, _
               CallingConvention:=CallingConvention.StdCall)> _
    Private Shared Function _ZN11QtEngineDll7randIntEv(ByRef u As String) As String
    End Function

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Now my qtcode goes as follows:

QtEngineDll::QtEngineDll(const char* url)
{
    m = url;
}
 
const char* QtEngineDll::randInt()
{
    QByteArray d(m);
    QString result = d.data();
    QString fileName = QDir::currentPath() + "/Test.txt";
    QFile file(fileName);
    file.open(QIODevice::Append | QIODevice::Text);
    file.write(result + "\n");
    return result;
}

QtEngineDll::QtEngineDll(const char* url)
{
    m = url;
}

const char* QtEngineDll::randInt()
{
    QByteArray d(m);
    QString result = d.data();
    QString fileName = QDir::currentPath() + "/Test.txt";
    QFile file(fileName);
    file.open(QIODevice::Append | QIODevice::Text);
    file.write(result + "\n");
    return result;
}

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But the file output is something like this:

[07/03/10 - 12:03:46],	Abhijit	U‰åVSƒìpE¸‰$èT

[07/03/10 - 12:03:46],	Abhijit	U‰åVSƒìpE¸‰$èT

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Can you pls tell me what is the wrong that I am committing in the code?

Thanks in advance.

[toutarrive]

QByteArray stores raw bytes (including '\0's) and traditional 8-bit '\0'-terminated strings.
You can't get Unicode character whit it.

[toutarrive]

Use instead QString::fromUtf8 ( const char * str, int size = -1 ) .
Read the Qt doc.

[abghosh]

Thanks toutarrive.

However if I use the following:

const char* test = "Abhijit";
    QByteArray d(test);
    result = QString::number(d.size());
    QString fileName = QDir::currentPath() + "/Test.txt";
    QFile file(fileName);
    file.open(QIODevice::Append | QIODevice::Text);
    file.write(QString(test) + "\n");
    return result;

const char* test = "Abhijit";
    QByteArray d(test);
    result = QString::number(d.size());
    QString fileName = QDir::currentPath() + "/Test.txt";
    QFile file(fileName);
    file.open(QIODevice::Append | QIODevice::Text);
    file.write(QString(test) + "\n");
    return result;

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everything is going fine. But if instead of defining test in the program itself, if I pass test value as an parameter from vb.net then some absurd result is thrown. Can anybody put some light on this?

Thanks in advance.

[Lesiok]

Can You guarantee that in QtEngineDll::randInt() pointer delivered to QtEngineDll constructor is steel point to this same data ?
Maybe it will be better to create QByteArray object in QtEngineDll constructor.

[abghosh]

Hi Lisiok

Can u pls demonstrate the same in this context.

Any way thnks for suggesting a better method.

[toutarrive]

I don't see in your code where you are handling the unicode characters.

[abghosh]

Hi

The problem as far as I have found is in passing the parameter may it be string or integer. The argument value is not at all passed properly. Even if I passed some integer value it is taking it as 1 and not the value passed actually.
Cant understand whether it is a problem in my vb.net call or the dll function definition.

I have attached the files required for building the DLL file in Qt 4. Note that the entry point name is taken from the dll file reader.

If I have committed some mistake in making the DLL file can you pls modify it.


Thanks in advance.

[ChrisW67]

I'm not familiar with mating .Net code to straight C++ code, but it seems that the parameter list here:

Private Shared Function _ZN11QtEngineDll7randIntEv(ByRef u As String) As String

Private Shared Function _ZN11QtEngineDll7randIntEv(ByRef u As String) As String

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(one parameter) doesn't match the one here:

const char* QtEngineDll::randInt()

const char* QtEngineDll::randInt()

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(no parameter, but probably requires an implied this pointer)
Any value passed by VB.Net in the u parameter has nowhere to go in the C++ (except perhaps being misinterpreted as a this pointer).

Other things to ponder: Your randInt() tries to dump a string set in the constructor to a file, and not a parameter passed to the method. Where is your object constructed? How is VB.Net setting a "this" pointer when it calls the randInt() method?

[abghosh]

Hi ChrisW67

The function mentioned by you is the older one. I have recently attached the new file where I just want to pass some integer value.
Passing integer value is also having error.

What I now think is to pass the parameter using some pointer. But I have no idea about reading pointer variables in Qt. Can you pls put some light on the same.

Thanks in advance.