I forgot how to turn a string into a double

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I accidentally deleted the bit of my code, that turns a string into a double, I rewrote it but it doesn't do what I want it to, and I forgot how this is new code bit:

double str2int(string test)
{
double qtest;
stringstream etest;
etest << test;
etest >> qtest;
cout<<qtest<<endl;
return qtest;
}

it works but doesn't convert stuff like a5 into a double?
ways to do that?
sorry for the rushed nature of this question, I have a bus to catch haha

What I have tried:

i've tried rewriting the code but it just gives the same result

Posted 2-Mar-22 18:26pm

Abdulrahmon Tijani

Updated 2-Mar-22 20:50pm

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_Asif_ 3-Mar-22 3:01am

as everyone mentioned "a5" is not double type.
"5" -> 5.00 because 5 as string can be converted into double as 5.00
But how "a" in "a5" will be converted into double?

3 solutions

Solution 1

The input value: a5 is not a valid argument to convert into double. It should throws an exception "invalid_argument"
Check the following link for conversion from string to double/float.
C++ String to float/double and vice-versa[^]

Posted 2-Mar-22 18:33pm

M Imran Ansari

Comments

Abdulrahmon Tijani 3-Mar-22 0:35am

as a string
also I'm not using stoi/stod(you know them) so it doesn't give an error

Solution 3

No big deal: simply use the stod of the standard library.

tip: check for the error cases

Posted 2-Mar-22 20:50pm

KarstenK

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OriginalGriff · Accepted Answer · 2022-03-02T19:57:00

You can't turn a string like "a5" into a double: it isn't a numeric value at all, and will throw an error in nearly every language, including C++.

To do that, you'd have to "strip out" the non-numeric data and convert that, but first think about the input value range and work out exactly what you want to convert it to.
For example, "a5p6" : what should that be? 56? 5.6? 6? 5? What about "5e6"? Should that be 5000000? Or 56? How about "e5"? Is that 5 or zero?

THink about where you get your data from and what it might actually represent: normally a "string based value" is a string for a reason!