In C, how to convert a floating-point number in a string to double ?

In C / C++, atof() is a dedicated function for converting strings to floats (or doubles). First, include stdlib.h:

#include <stdlib.h>

Then, simply convert strings to floats (or doubles) :

char string[] = "10.66814";
float value = atof(string);

Test the previous code online on OneCompiler.

If the first sequence of non-whitespace characters in string does not form a valid floating-point number, the function atof() returns 0.0.

In C / C++, there is a dedicated function for converting strings to doubles : atof(). First, you'll need to include stdlib.h :

#include <stdlib.h>

Then, simply convert string to double (or float) :

char string[] = "10.66814";
double value = atof(string);

Test the previous code online on OneCompiler.

If the first sequence of non-whitespace characters in string does not form a valid floating-point number, the function atof() returns 0.0.

In C / C++, there is a dedicated function for converting strings to floats : atof(). First, you'll need to include stdlib.h :

#include <stdlib.h>

Then, simply convert string to float :

char string[] = "10.66814";
float value = atof(string);

Test the previous code online on OneCompiler.

If the first sequence of non-whitespace characters in string does not form a valid floating-point number, the function atof() returns 0.0.