URLDownloadToFile string

I am trying to use URLDownloadToFile to download from a given URL. I am using the following function:

URLDownloadToFile Function ()

Here is my code:

Code:

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#include <urlmon.h>
#include <iostream>
#pragma comment(lib, "urlmon.lib")
#include <stdio.h>
#include <string>
#include <windows.h>

using namespace std;

int main (){

        string url = "http://www.google.com/";
        URLDownloadToFile( NULL, url, "index.html", 0, NULL );

        return 0;
}

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I get the following:

Code:

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error C2664: 'URLDownloadToFileA' : cannot convert parameter 2 from 'std::string' to 'LPCSTR'

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This seems like a simple error - what do I need to do to correct it?

Thanks.

URLDownloadToFile takes a const char * as its second argument, not a string. That what that error is telling you. Lucky for you the std::string class has the c_str() function to convert it to a const char *.

Thanks - that worked a treat. However, it all seems to break down when I try to use strings in Win32 programs. Is there a tutorial on how I could go about doing this? For example, if I have this code:

Code:

---

#include <windows.h>
#include <cstdio>
#include "resource.h"
#include <urlmon.h>
#include <iostream>
#pragma comment(lib, "urlmon.lib")
#include <string>
#include <cstring>
#include <stdio.h>

string url = "http://";

BOOL CALLBACK ToolDlgProc(HWND hwnd, UINT Message, WPARAM wParam, LPARAM lParam)
{
        switch(Message)
        {
                case WM_COMMAND:
                        switch(LOWORD(wParam))
                        {
                                case IDC_DOWNLOAD:      //Pressing download button.
                                        {
int len = GetWindowTextLength(GetDlgItem(hwnd, IDC_URL)); //Extracting the rest of the web address from a text box.

char* buf;
buf = (char*)GlobalAlloc(GPTR, len + 1);
GetDlgItemText(hwnd, IDC_URL, buf, len + 1);        //Assigning the URL to 'buf'.
string final = url + atof(buf);  //Adding the rest of the web address to 'http://'
const char *finalurl = final.c_str ( );    //Converting to c_str();
URLDownloadToFile( NULL, finalurl, "index.html", 0, NULL );        //Downloading it.
ShellExecute(NULL, "open", "index.html", NULL, NULL, SW_SHOWNORMAL);      //Opening it.

GlobalFree(buf);
break;

}               

                                case IDC_CLOSE:
                                        EndDialog(hwnd, 0);
                                break;
                               
                        }
                break;

                case WM_CLOSE:
                        EndDialog(hwnd, 0);
                    break;

                default:
                        return FALSE;
        }
        return TRUE;
}

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
        LPSTR lpCmdLine, int nCmdShow)
{
        return DialogBox(hInstance, MAKEINTRESOURCE(IDD_DOWNLOADER), NULL, ToolDlgProc);
}

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When I try to compile this, I get errors such as error C2784, error C2782 and error C2676. It looks like I am doing something very wrong (I am guessing that you need to use a different syntax for strings in Win32).

Thanks.

The Win32 API is written in C, not C++. Therefore, if you're going to use std::string, you will need to convert to C strings (through c_str()) to call functions requiring char *s. Don't give Visual Studio compiler codes only...we don't have them memorized! Give the entire error along with the appropriate lines.

Thanks for the response - sorry about the errors - each one was about 5 lines long and just looked like gibberish to me!

So I basically need to convert each string to a c_string before using it, eg:

Code:

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std::string url = "http://";
const char *url2 = url.c_str ( );

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...and then use:

Code:

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std::string final = url2 + atof(buf);
const char *final2 = final.c_str ( );

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...and it should work? Thanks.

...that seems to have got rid of most of the errors, but now I get this error:

Code:

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error C2111: '+' : pointer addition requires integral operand

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This is referring to this line:

Code:

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string final = url + atof(buf);

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Once again - I guess I am just doing something wrong that doesn't work in Win32.

*Edited*

Code:

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std::string final = url + atof(buf);

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atof converts string to floating-point value.

Code:

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std::string final = url + buf;

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Thanks - I tried that too, but now I get:

Code:

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error C2110: '+' : cannot add two pointers

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Never mind - I changed it to this:

Code:

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std::string final;
final += "http://";
final += buf;
const char *finalurl = final.c_str ( );

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...and it seems to work now.