Why is "string" abbreviated into "a" in standard C library function names?

Question

Standard C utility library stdlib.h has these function names:

(String as 'a'):

• atof
• atoi
• itoa

(String as 'str'):

• strtoul
• strtol
• strtod

Why is a string sometimes called an "a" and sometimes called an "str"?

Answer 1

a stands for ASCII, so in atoi it is ASCII to integer. See here. The ato family of functions have been deprecated by str functions.