implicit declaration of function 'execle' error

Question

I keep getting

implicit declaration of function \'execle\' is invalid in C99

when compiling the code below. What am I missing?

Answer 1

In C99, the implicit declaration of a function is not allowed. That means, the compiler should be aware of the function signature before it encounters a call to that function. This can be achieved two ways: 

1. Define the function before using it.
2. Provide a forward declaration of the function and define it later.

Usually, the function signature is provided as a forward declaration through the header files.

As per the man page of execle(), you need to include unistd.h to get the forward declaration.