Converting string to float

[elpichi]

i'm having a hard time finding the right way to convert from string to a float.
I'm making a program that makes a file that logs the profits of a person
the problem comes when i try to get the number which could be anywhere in the file except it has "The ending balance for the account is: $399.09" or any other float. i managed to make a loop that searches through the entire file for those exact words, but i get a string and i need that info in a float variable.

Any advice would be super helpful, thanks.

float balance=0;
string name, line, clean, number;
stringstream streamer;
string match = "The ending balance for the account is: ";
cout << setprecision(2);
//check if file exist and create a new file if there isn't any
ifstream inbudget;
inbudget.open("budget.dat", ios::ate);
if(inbudget.is_open())
{
while(inbudget)
{

int pos = -1;
getline(inbudget, line);
pos = line.find('$');
clean = line.substr(0, pos);
line = line.substr(pos+1);

if(clean == match)
number = line;
}

cout << number << endl;
streamer >> number;

inbudget.close();
}

while displaying the number before converting it shows exactly what i want, but somehow it turns into a 1.8 or 1.9 after streamer does its job.

[Can+~]

http://www.cplusplus.com/reference/clibrary/cstdlib/atof.html

You could use some indentation in your code btw.

[Zugzwang]

http://www.cplusplus.com/reference/clibrary/cstdlib/atof.html

You could use some indentation in your code btw.

Another alternative is to use an istringstream (http://www.cplusplus.com/reference/iostream/istringstream/istringstream.html) (this is more C++ style). Make sure that you use the fail() method to check if the conversion was successful afterwards.

This is an example. Give a number as parameter to the program and it will be multiplied by 2.

// Multiply by 2
#include <sstream>
#include <iostream>

int main(int argsv, char **args) {
if (argsv<2) {
std::cout << "No number given" << std::endl;
return 1;
}

std::istringstream in(args[1]);

float number;
in >> number;

if (in.fail()) {
std::cout << "No valid number given" << std::endl;
return 1;
}

std::cout << "Multiplied by two, this is: " << number*2 << std::endl;
return 0;
}

[elpichi]

For some reason atof() doesn't work for me, an error compiling got me stumped saying it could not convert a const char into a char, but istringstream works great, though it doesn't convert to floats, I converted the number and the decimals separately, then added them together.
Thanks for the answers

[Jessehk]

I like writing a little wrapper for converting from strings to other types.
I'm not exactly sure what you mean about floats not working...


#include <iostream>
#include <string>
#include <sstream>
#include <stdexcept>

template <typename T>
T fromString( const std::string &str ) {
std::stringstream ss( str );
T result;

if ( ! (ss >> result) )
throw std::invalid_argument( "Conversion error" );

return result;
}

int main() {
try {
float pi = fromString<float>( "3.14159" );
} catch ( std::exception &e ) {
std::cout << e.what() << std::endl;
}
}

[elpichi]

Whoa sorry a little piece of code was making me go nuts.
seems like setting precision to 2 messed up the output of my conversions so i was getting weird things like 2e+02 etc.

This is how i got it.


float balance=0;
string name, line;
string match = "The ending balance for the account is: ";
//check if file exist and create a new file if there isn't any
ifstream inbudget;
inbudget.open("budget.dat");
if(inbudget.is_open())
{
//if file exists it looks in the whole file for phrases similar to match
while(inbudget)
{
int pos = -1; //location of pointer
getline(inbudget, line); //gets a line from the file and puts it inside line as a string
pos = line.find('$'); //sets location of posible places where money is represented

if(match == line.substr(0, pos)) //if a match comes up the number converted into a float and saved
balance = converter(line.substr(pos+1));

}
inbudget.close();
}


And this is how my function for convertion.

float converter(string number)
{
float val;
string stringvalues;

istringstream iss (number,istringstream::in);
iss >> val;

return val;
}

don't really need to check for successful conversions since the file is only going to be edited by the program itself.