Converting string to float

CT++ · #1 09-May-2005, 23:48

I'm working on a program that takes a bunch of valued from a .txt file, using getline. Each line is a string, and is separated into sub strings via a loop.

For example:
11 1111 111 1 111

I can get things working perfectly up to the point where it takes a line like above. It finds the first blank space, and copies every location from 0 to the number of the white space into a temporary string. Then it snips off the leading white space, and runs the loop again.

When it runs, it would print out:

Code:

Each time through, it snips off just what I want, and keeps going till the string is empty.

CPP / C++ / C Code:

  -------------------------

void StripNums(vector<string> vect)
{
	cout << "\n\n\n------- Splitter ---------------\n";
	string temp;
	for (int i=0; i < vect.size(); i++)		//	for every row of data
	{
		while (vect[i].empty()!=true)
	   {
			temp.clear();							//	Clear the temp string
			int marker = 0;							//	Set marker to zero
			marker= vect[i].find(' ');				//	Set the end of the first digit to the first whitespace
			if (marker < 1)							//	If there is no whitespace...
				marker=vect[i].size();				//	...set the end of first digit to the end of the string
			cout << "marker: " << marker << endl;	//
			temp = vect[i].substr(0,marker);		//	Set the temp string to the chars between the start of the string and the marker
			cout << "temp: " << temp << endl;		//
			vect[i].erase(0, temp.size()+1);		//	Erase the chars that were put into the temp string, as well as the leading whitespace
			cout <<"xxxxxxxx" << atof(temp);
			cout << "\nTemp is now:" << temp << endl;
		}
		cout << endl; 
	}
}

-------------------------------

The problem that I am having (and it's driving me nuts) is that I cannot convert the string to a float... or an integer, or anything. According to my textbook (Gaddis), it's the easiest thing in the world. The syntax the book lists is just:

CPP / C++ / C Code:

atof(string_name);

...but it doesn't work. I've tried making an integer/double/float and setting it equal to the string, like:

CPP / C++ / C Code:

float tempFloat;
tempFloat=atof(temp);

Plus similar variations, but I always get an error that tells me:

"cannot convert 'std::string' to 'const char*' for argument '1' to 'double atof(const char*)'"

I've been going bonkers searching the web for how to do this, and I think maybe I'm trying to convert a dynamic variable into a static one, but I can't for the life of me find an example of some way to fix things that helps me out. From what the book shows me, I can't see why if my temp string is a string, I can't just use atof or atoi to convert it into something I can actually do math with :-?

I've hit the end of my rope, and was hoping someone here might be able to help me out?

P.S. Yes, I do have the <cstdlib> include file in the program

LuciWiz · #2 10-May-2005, 00:10

Quote:

Originally Posted by CT++

"cannot convert 'std::string' to 'const char*' for argument '1' to 'double atof(const char*)'"

So, the definition of atof looks like this:

CPP / C++ / C Code:

double  atof ( const char * string );

It expects a const char * parameter, but you feed it a std::string. In order to convert it to a C-style array (char *), use the c_str() member:

CPP / C++ / C Code:

string_name.c_str();

Try it now!

Best regards,
Lucian

CT++ · #3 10-May-2005, 12:29

Thank you! I had never used that before, but I looked it up, and after some trial and error, got it to work perfectly! I really appreciate your help

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