C parsing double from argument strings

I'm trying to parse an argument value in C and convert the number to a double value. I have:

char *stringEnd; double num = strtod("123.0", &stringEnd);

I used "123.0" just t开发者_StackOverflow中文版o test the function, but it always returns a value of 0.0. Does anybody know what I'm doing wrong?

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Are you including the relevant header? ie: #include <stdlib.h>

First though (and you should be doing this all the time anyway), try compiling with all warnings on (-Wall on GCC).

If you get a warning about strtod being undefined, that shows where the problem is coming from.

This is a nasty one, because C will implicitly declare any function it doesn't have a prototype for as returning int!

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You can use sscanf.

double num;
sscanf("123.0", "%lf", &num);

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You if have to use strtod in order to use:

double num = strtod("123.0", NULL);

you can also use sscanf

double num;    
sscanf("123.0", "%lf", &num);

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You need to #include stdlib.h.

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In which language is your operating system? I'm not sure how the C function strtod reacts, but I know that the equivalent delphi function takes the settings of the operating system into account. Some languages (french, german, ...) use a "," instead of a "." as decimal separator.