Where did the name `atoi` come from?

c naming-conventions atoi
Earlz picture Earlz · May 26, 2010 · Viewed 18k times · Source

In the C language where did they come up with the name atoi for converting a string to an integer? The only thing I can think of is Array To Integer for an acronym but that doesn't really make sense.

Answer

Mark Rushakoff picture Mark Rushakoff · May 26, 2010

It means Ascii to Integer. Likewise, you can have atol for Ascii to Long, atof for Ascii to Float, etc.

A Google search for 'atoi "ascii to integer"' confirms this on several pages.

I'm having trouble finding any official source on it... but in this listing of man pages from Third Edition Unix (1973) collected by Dennis Ritchie himself, it does contain the line:

atoi(III): convert ASCII to integer

In fact, even the first edition Unix (ca 1971) man pages list atoi as meaning Ascii to Integer.

So even if there isn't any documentation more official than man pages indicating that atoi means Ascii to Integer (I suspect there is and I just haven't been able to locate it), it's been Ascii to Integer by convention at least since 1971.

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