Reading numbers from file to string to array - c++

Question

I am reading numbers from a file, say:
1 2 3 4 5
I want to read this data from a file into a string into an array for further processing. Here's what I've done:
float *ar = nullptr;
while (getline(inFile, line))
{
ar = new float[line.length()];
for (unsigned int i = 0; i < line.length(); i++)
{
stringstream ss(line);
ss >> ar[i];
}
}
unsigned int arsize = sizeof(ar) / sizeof(ar[0]);
delete ar;
Suffice it to say that it works insofar it only gets the first value from the file. How do I get the array to be input ALL the values? I debugged the program and I can confirm that line has all the necessary values; but the float array doesn't. Please help, thanks!

Answer 1

line.length() is the number of characters in the line, not the number of words/numbers/whatevers.
Use a vector, which can be easily resized, rather than trying to juggle pointers.
std::vector<float> ar;
std::stringstream ss(line);
float value;
while (ss >> value) { // or (inFile >> value) if you don't care about lines
ar.push_back(value);
}
The size is now available as ar.size(); your use of sizeof wouldn't work since ar is a pointer, not an array.

Answer 2

The easiest option is to use the standard library and its streams.
$ cat test.data
1.2 2.4 3 4 5
Given the file you can use the stream library like this:
#include <fstream>
#include <vector>
#include <iostream>
int main(int argc, char *argv[]) {
std::ifstream file("./test.data", std::ios::in);
std::vector<float> res(std::istream_iterator<float>(file),
(std::istream_iterator<float>()));
// and print it to the standard out
std::copy(std::begin(res), std::end(res),
std::ostream_iterator<float>(std::cout, "\n"));
return 0;
}

Answer 3

I ran into this problem earlier when I wanted to extract data line by line from a file to fill my sql database that I wanted to use.
There are many solutions to this specific problem such as:
The solution is using stringstream with a while statement to put data from file into the array with a while statement
//EDIT
While statement with getline
//This solution isn't very complex and is pretty easy to use.
New Improved simple solution:
#include <iostream>
#include <fstream>
#include <string>
#include <vector>
using namespace std;
int main()
{
ifstream line;
line.open("__FILENAME__");
string s;
vector<string> lines;
while(getline(line, s))
{
lines.push_back(s);
}
for(int i = 0;i < lines.size();i++)
{
cout << lines[i] << " ";
}
return 0;
}
compiled code to check - http://ideone.com/kBX45a

Answer 4

What about atof?
std::string value = "1.5";
auto converted = atof ( value.c_str() );
Rather complete:
while ( std::getline ( string ) )
{
std::vector < std::string > splitted;
boost::split ( splitted, line, boost::is_any_of ( " " ) );
std::vector < double > values;
for ( auto const& str: splitted ) {
auto value = atof ( str.c_str() );
values.push_back ( value );
}
}