c - atof always returns 0.0 under Linux platform

Question

The code is as follows {code...} The result is always 0.000000, not 123.3, why?

迷茫 · Answer

Because you didn’t include stdlib.h (　゜ロ゜)”
This is a hidden pit. Because you did not include the header file, there is no function declaration. Without a function declaration, the default return value of the library function is int type.
If you add -Wall when compiling, it will clearly tell you that it is not declared.