如何使用cin从输入的字符串中提取特定的数值？

Question

1U = 1.2A
1U = 2.3B
1U = 3.4C
1U = 4.5D
1U = 5.6E
1U = 6.7F
1U = 7.8G

The code above is the input. Is there a way to only extract the numbers from each line? For example, in the first line, the only values I want is 1.2, not the "1U = " or the A after it. I tried using regular cin and getline(), but they detect a string so they cannot receive any input. I also tried using cin.ignore but I believe I used it incorrectly. This is what I have so far:

 double temp;
 cin.ignore(numeric_limits<streamsize>::max(), '\n');
 cin >> temp;

Answer 1

cin.ignore(numeric_limits<streamsize>::max(), '\n');

Will ignore a whole line. But

cin.ignore(numeric_limits<streamsize>::max(), '=');

will ignore everything up to = so

1U = 1.2A
1U = 2.3B
1U = 3.4C

would become

 1.2A
1U = 2.3B
1U = 3.4C

Now you can

cin >> temp;

Which would read skip whitespace 1.2 into temp and stop as soon as it finds something that cannot be a double .

A
1U = 2.3B
1U = 3.4C

then you loop back around to

cin.ignore(numeric_limits<streamsize>::max(), '=');

which will leave

 2.3B
1U = 3.4C

and

cin >> temp;

grabs 2.8 and then repeat again.

Code for this could look like

while (cin.ignore(numeric_limits<streamsize>::max(), '=') &&
       cin >> temp)
{
    // use temp
}