Reading text file into an array

I am new in c++.

I need to read a text file containing something like this data:

0.6662 0.5435 0.5545 0.55487
0.4346 0.7698 0.8965 0.56438
...
...

It is 100 rows and 4 columns

I write the following codes:

#include
#include
#include

using namespace std;
//The main program
int main()
{
double str[100][4];
string xx;
ifstream myfile("testfile.txt");
while(!myfile.eof()){
getline(myfile, xx, ' ');
for (int i = 0; i < 100; i++){
for (int j = 0; j < 4; j++){
str[j] = atof(xx.c_str());
}
}
}
myfile.close();
system("pause");
}

I checked the matrix str, it just give me first column repeatedly. I am no where close to the answer. Please help...