How to convert string to float?

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Use atof() or strtof()* instead:

printf("float value : %4.8f\n" ,atof(s)); 
printf("float value : %4.8f\n" ,strtof(s, NULL));

http://www.cplusplus.com/reference/clibrary/cstdlib/atof/
http://www.cplusplus.com/reference/cstdlib/strtof/

  • atoll() is meant for integers.
  • atof()/strtof() is for floats.

The reason why you only get 4.00 with atoll() is because it stops parsing when it finds the first non-digit.

*Note that strtof() requires C99 or C++11.

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