c_str() problem

**h3ro** · 05-14-2007

Hallo,

I try to do this:
faceList.push_back(atoi( line[i].c_str() ));

But I get an error saying that c_str() is not declared, but I have already used it and then there is no error.

This works:
(float)atof(vertexString[0].c_str())

Any ideas?

**Shakti** · 05-14-2007

Could you give us the smallest example of a program that doesnt work?

**Daved** · 05-14-2007

Is line an array or vector of strings? If it is, then make sure you #include <string>. If not, then c_str() won't work on an object that is not a string.

Of course, a stringstream is often better for conversions than atoi.

Also, if line is a string, but you only want to convert an individual character to a number, then just subtract the '0' character:

Code:

int num = line[i] - '0';

**h3ro** · 05-14-2007

Sorry for the limited information

This is the function I am working on now, where c_str() does not work

Code:

std::vector<int> loadFaceConnections(std::string line)
{
     //stff
     std::vector <int> faceList;
     for (int i = 2; i <= line.size(); i++)
     {
         if (line[i] != ' ' && line[i] != '/')
         {
             faceList.push_back(atoi( line[i].c_str() ));
         }
     }
     
     for (int x = 0; x < faceList.size(); x++)
     {
         std::cout << faceList[x] << std::endl;
     }
     
     return faceList;
}

But I find it kind of weird that c_str() is not declared (according to compiler) as it works in this function that is part of the same file/program

Code:

Vector3D processVertex(std::string line)
{
         std::string vertexString[3];
         int x = 0;
         
         for (int i = 2; i <= line.size(); i++)
         {
             if ( line[i] == ' ')
             {
                  x++;
             }
             else
             {
                 // add to same cord
                 vertexString[x].push_back(line[i]);
             }
         }
         
         
         // Convert the string into a number
         Vector3D vertex( (float)atof(vertexString[0].c_str()),
                          (float)atof(vertexString[1].c_str()),
                          (float)atof(vertexString[2].c_str())
                          );
         
         return vertex;
}

Thanks

**Shakti** · 05-14-2007

When you access line[i] in your first example you access the character at index i in the string object line. that character is of type char, and can thus not have the function c_str() in it.

**laserlight** · 05-14-2007

In loadFaceConnections(), line is a std::string, so line[i] is a char, and a char does not have a c_str() member function. Perhaps you wanted to pass a vector of strings instead?

**Daved** · 05-14-2007

So what are you trying to do there? Obviously, line is a string, and line[i] is a character and atoi only works with a string of characters.

Are you trying to convert a single digit? If so, see my edited post above.

Are you just trying to extract a number with possibly more than one digit from a string? If so, you'll need to parse the line a bit more. You can use a stringstream, or maybe find() and substr(). It depends on what the line looks like and how you want to parse it. Give the format of the line and an example if you need further help.

**h3ro** · 05-14-2007

I am trying to read some info from a file I have. The format for the data is:
...
f 1/1/1 2/2/2 3/3/3
f 2/2/2 4/4/4 3/3/3
...

The numbers can be anything but they are always a int.

If the line starts with the character f I call the loadFaceConnection() function.

I know that as the loop is now it will only take single number digits, but I did like this so that I had somewhere to start, but I got stuck.

Thanks for the help so far

**Daved** · 05-14-2007

Do you know how to read that line in and get the integers if you were using cin instead of having the text in a string?

I would place the line into a stringstream and parse it that way since you know the exact format. The code is exactly the same as you'd use for cin except you'd use your stringstream variable instead. Practice first with a simple program and then when it is working move the code into your bigger application.

**h3ro** · 05-14-2007

Do you know how to read that line in and get the integers if you were using cin instead of having the text in a string?

Kind of embarrassing, but I dont know how. Reading trough some stuff now

Edit:

I have made something that works now, thanks for all help.

Code:

 std::vector<int> loadFaceConnections(std::string line)
{
     std::vector <int> faceList;
     std::string tempString;
     int tempNumber = 0;
     
     for (int i = 2; i <= line.size(); i++)
     {
         // If the line is not empty and does not have a '/' sign it contains
         // a number. Add it to the temp string
         if (line[i] != ' ' && line[i] != '/')
         {
             // Add the number to the tempString
             tempString.push_back(line[i]);
         }
         else
         {
             // If the string is not empty we create a integer out of it
             if (tempString.size() != 0)
             {
                 // Create a number
                 std::istringstream stringNumber (tempString);
                 stringNumber >> tempNumber;
                 
                 // Add the number to the vector
                 faceList.push_back(tempNumber);
                 
                 // Clear the tempString
                 tempString.clear();
             }
         }
     }
     
     // Print the thing, for debugging purpose
     for (int x = 0; x < faceList.size(); x++)
     {
         std::cout << faceList[x] << std::endl;
     }
     std::cout << std::endl;
     
     
     return faceList;
}

This work fine, except that the last number never gets inputed

**vart** · 05-14-2007

This work fine, except that the last number never gets inputed

This is because when you exit the for loop - tempString can contain data that you never process

**h3ro** · 05-15-2007

This is because when you exit the for loop - tempString can contain data that you never process

I know, I assume that I have to else statement one more time, but not sure how to accomplish this. I have tried to increase the size of line.size() but that did not work

**vart** · 05-15-2007

Code:

      for (int i = 2; i <= line.size(); i++)
     {
         // If the line is not empty and does not have a '/' sign it contains
         // a number. Add it to the temp string
         if (line[i] != ' ' && line[i] != '/')
         {
             // Add the number to the tempString
             tempString.push_back(line[i]);
         }
         else
         {
             // If the string is not empty we create a integer out of it
             if (tempString.size() != 0)
             {
                 // Create a number
                 std::istringstream stringNumber (tempString);
                 stringNumber >> tempNumber;
                 
                 // Add the number to the vector
                 faceList.push_back(tempNumber);
                 
                 // Clear the tempString
                 tempString.clear();
             }
         }
     }
     if (tempString.size() != 0)
    {
        // Create a number
        std::istringstream stringNumber (tempString);
        stringNumber >> tempNumber;
              
        // Add the number to the vector
        faceList.push_back(tempNumber);
                 
    }

FOR EXAMPLE

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