optimal way to convert string to double?

Question

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converting a string into a double

What is the optimal way to convert string to double ? am using sstream but I feel it is not that fast.. is there a faster wawy without using any external libraries or sth.

"I feel that it is not fast" - how fast is it, and how fast do you need it to be? — Oliver Charlesworth, Jul 13 '12 at 13:42
Is there a pattern to these strings that will be converted to doubles? If so, the best way may be to hand roll your own function. — Nick Babcock, Jul 13 '12 at 13:43
Please see the similar Q/A http://stackoverflow.com/questions/392981/how-can-i-convert-string-to-double-in-c — Derui Si, Jul 13 '12 at 14:57

score 3 · Accepted Answer · answered Jul 13 '12 at 13:44

3

strtod() will have less overhead than using sstream.

#include <stdlib.h>

char * s = ...;
double d = strtod(s, 0);

answered Jul 13 '12 at 13:44

Ernest Friedman-Hill

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Of course, if his input is in a `string`, he'll have to use `c_str()` to get it. And it needs some error checking. – James Kanze Jul 13 '12 at 13:47

score 0 · Answer 2 · answered Jul 13 '12 at 13:55

0

you can use boost library lexical cast They also include performance test results on their documentation page boost lexical cast

cheers

answered Jul 13 '12 at 13:55

Moataz Elmasry

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@Mike: Early versions did, newer versions have overrides for a number of types, including double. It only falls back to using the stringstream if it doesn't have its own mechanism for performing the conversion. – Dave S Jul 13 '12 at 14:36
@Mike, thats right, in their test results they are comparing their method to sstream and showing that lexicalcast is f#aster – Moataz Elmasry Jul 13 '12 at 14:42

optimal way to convert string to double?

2 Answers2