printf() group function summary

is to format the string, see the manual for details

1. The printf()  function outputs a formatted string. (to print)

2. The sprintf()  function writes the formatted string into the variable (note: the same as the printf() function, but does not print)

3. The fprint()  function writes the formatted string to the specified output stream (for example: file or database)

4 vprintf() , v sprintf() , v fprint(), these three functions are the same as the above three, just add v, and the parameters are placed in the array.