Be Careful when Using printf()’s return value

Functions from the printf() family typically return the number of printed characters. This value can be used to determine how many characters are needed on the output medium for a given input to a format string. Depending on your C library, printf() may use an internal dynamic buffer, and memory allocation can fail. In such cases, the function returns a negative number. Therefore, we recommend to always check the return value for positivity when using it in a computation.