convert a vector<string> into a string

[Joelito]

This is my vector:

vector<string> ext;
exts.push_back(TEXT("png"));
exts.push_back(TEXT("jpg"));
exts.push_back(TEXT("gif"));
exts.push_back(TEXT("bmp"));

I wan to create the vector into a string to have like the OPENFILENAME::lpstrFilter, that would be something like:

string final = "All files supported\0*.png;*.jpg;*.gif;*.bmp\0\0";

Right now I'm using something like this:

vector<string> ext;
	stringstream str;
	ext.push_back("png");
	ext.push_back("jpg");
	ext.push_back("bmp");
	ext.push_back("gif");
	size_t len = ext.size();
	str << "All files supported\0";
	for (size_t pos = 0; pos != len; pos++ )
    {
        str << "*." << ext[pos] << ";";
    }
str << "\0\0";
	// use str.str().c_str() as filter

But doesn't work
any ideas?

[whiteflags]

Try using something other than \0 as a delimiter.

[anon]

I guess the null characters are not inserted because in a C-style string (string literal) they mean the end of string.

You can use string concatenation, and take care with inserting null characters in the string (cannot be done as part of a string literal).

#include <vector>
#include <string>
#include <iostream>
using namespace std;
int main()
{
    vector<string> ext;
    ext.push_back("png");
    ext.push_back("jpg");
    ext.push_back("bmp");
    ext.push_back("gif");
    size_t len = ext.size();
    string filter = "All files supported";
    filter += '\0';
    for (size_t pos = 0; pos != ext.size(); pos++ )
    {
        filter += "*." + ext[pos] + (pos + 1 < len ? ";" : "");
    }
    filter += string(2, '\0'); //two more null characters
    std::cout << "'" << filter << "'";
}

Try using something other than \0 as a delimiter.

That's how the API likes it.

[whiteflags]

I don't know what OP expected to happen, but when I ran his code, it did exactly what yours would do anon. That is, str.str().c_string() is like a concatenated string. So my only guess was that he saw something he didn't expect, which would only require using a different delimiter to see the effect.

[anon]

I hardly believe it would be the same. In my code the resulting string is 45 characters, OP's resulting string is 43 (no null characters, one extra semicolon).

Those two have the exact same effect:

str << "\0\0";
str << "";

Neither one inserts any characters in the stream.

If you use a different character, the problem will naturally go away, except your string will contain wrong delimiters. (You could replace those later.)

[grumpy]

The interaction between the std::string type and strings that contain a zero byte is a bit fiddly, if you rely on them being more than 1. I'd actually use a vector as an intermediary.

    // untested code follows - written to show idea, not guaranteed correct

    char *tempfilter = "All files supported";
    
    std::vector<char> filter(0);
    filter.insert(filter.end(), tempfilter, tempfilter + strlen(tempfilter));   //  this takes the first '\0' for the ride
    for (std::vector<std::string>::const_iterator i = ext.begin(), end = ext.end(); i != end; ++i)
    {
           if (i->length() > 0)
           {
                  std::string temp = "*.";
                  temp += *i;
                  if (i + 1 != end) temp += ';'

                  filter.insert(filter.end(), temp.begin(), temp.end());
           }
    }
    filter.insert(filter.end(), '\0');
    filter.insert(filter.end(), '\0');
 
    std::string filter_to_use(filter.begin(), filter.end());

Note that printing the filter out (std::cout << filter) will only print to the first null character - by convention.

[Elysia]

I believe you missed a curly brace in there. Also, the end of the string should be double null terminated.

[Joelito]

Thanks, guys...I read about map and googled around and I came with this:

ustring CWnd::MakeFilter()
{
    /* mapped the file extensions that we want to use */
    m_Filtro["Archivos PNG"] = "png";
	m_Filtro["Archivos JPEG"] = "jpg";
	m_Filtro["Archivos GIF"] = "gif";
	m_Filtro["Archivos BMP"] = "bmp";
	/* begin filter maker */
    stringstream str;
    str << "Todos los soportados|";
    MapFiltro::iterator it;
    size_t len = m_Filtro.size();
    size_t pos = 0;
    for (it = m_Filtro.begin(); it != m_Filtro.end(); it++,pos++)
    {
        str << "*." << it->second << (pos < len-1 ? ";" : "");
    }
    str << "|";
    for (it = m_Filtro.begin(); it != m_Filtro.end(); it++)
    {
        str << it->first << "|*." << it->second << "|";
    }
    str << "|";
    ustring final = str.str();
    replace(final.begin(),final.end(),'|','\0');
    return final;
}