fstream dll in windows

[eddy]

Hello,

I'm creating a simple dll to interface with excel (a function to convert units), I know the code works because I have changed the source so that it is an executable and it works fine
When I try to use the below code in for the dll application for some reason the fstream (code line ifstream T(fpath.c_str(), ifstream::in);) does not work, the object is not created. I don't understand why the ifstream object can not be created, any help would be greatly appreciated.

Thanks in advance,
Ed

Below is part of the source:

include "dll.h"

include <windows.h>

include <iostream>

include <fstream>

include <sstream>

include <string>

include <vector>

include <wtypes.h>

include "units.h"

static std::vector<Unit_item> dunits;
int Load_flag=0;

using namespace std;
// Function to read file
int file_read(string fpath)
{

ifstream T(fpath.c_str(), ifstream::in);
Unit_item tempholder;
string ch="";
string version= "";
string header = "";
string d_temp = "";
int index = 1;

if (!T)
{
    //
    MessageBox (NULL,  "Could not Open File." , "Msgbox", 0);
    return 0;
}
int flen =0;
getline(T,version);
getline(T,header);
while(!T.eof())
{
    getline(T,ch);
    istringstream stream(ch);
    stream >> tempholder.units;
    stream >> tempholder.category;
    stream >> tempholder.factor;
    stream >> tempholder.offset;
    while (stream >> d_temp) {
        if (index >= 2)
        {
             tempholder.description += " " + d_temp;
        }
        else
        {
             tempholder.description = d_temp;
        }
        index ++;
    }
    dunits.push_back(tempholder);
    index=1;
    flen ++;
}
T.close();
T.clear();
Load_flag=1;
return 1;

}

DllClass::DllClass()
{

}

DllClass::~DllClass ()
{

}

BOOL APIENTRY DllMain (HINSTANCE hInst / Library instance handle. / ,
DWORD reason / Reason this function is being called. / ,
LPVOID reserved / Not used. / )
{
switch (reason)
{
case DLL_PROCESS_ATTACH:
break;

  case DLL_PROCESS_DETACH:
    break;

  case DLL_THREAD_ATTACH:
    break;

  case DLL_THREAD_DETACH:
    break;
}

/* Returns TRUE on success, FALSE on failure */
return TRUE;

}

//Function to Convert units
declspec(dllexport) double stdcall Unit_Convert(double init_value, BSTR ptr_initval, BSTR ptr_finalval)
{
string intemp="";
string finaltemp="";
if(!ptr_initval || !ptr_finalval) //ShouldneverbeNULL,but...
return 0; //ReturnVBFalse
if(!ptr_initval || !ptr_finalval) //Isstringinitialised?
return 0; //ReturnVBFalseifnot
for(int i=0;;i++)
{
if(!((char)(ptr_initval))[i]){
break;
}
intemp += ((char)(ptr_initval))[i];
}
for(int i=0;;i++)
{
if(!((char)(ptr_finalval))[i]){
break;
}
finaltemp += ((char)(*ptr_finalval))[i];
}
if (Load_flag == 0){
string fname = "t2.fac";
int file_flag;
file_flag = file_read(fname);
}
int j=unit_find(intemp);
int z=unit_find(finaltemp);
TCHAR numstr [ 32 ];
sprintf(numstr,"%.4f",z);
MessageBox (NULL, numstr ,"test" , 0);
double new_factor= dunits[j].factor * dunits[z].factor;
return new_factor;
}

[cpns]

The usual reason for failure is simply that the file does not exist. Have you tried calling it with a fully specified path (such as "c:\mydatafolder\t2.fac" for example)? If that works (with the file in the appropriate folder), then it is a simple case of your current working folder not being the same as your data folder at the time the code is executed.

Clifford

[cpns]

As an aside, note that DLL interfaces with C++ linkage are not portable amongst compilers, so other development tools may not be able to use your DLL.

[eddy]

Thank you Clifford,

I had tried before with the full path location but didn't realize you needed to double the "\&quot; in the string. Adding the full path solved the problem.

Thanks,
Ed

[cpns]

'\' is teh escape character in C/C++ used for placing 'invisible' characters such as tab ('\t') and newline ('\n') into string and character constants. How a single '\' is interpreted depends on what follows it. My example without the '\' escape sequences:

"c:\mydatafolder\t2.fac"

would be interpreted as:

"c:ydatafolder<TAB>2.fac"

Most modern Windows compilers will accept Unix style forward-slash ('/') folder delimiters, which need not (and should not) be doubled up.

Clifford