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Revision as of 13:05, 19 August 2010 by 1exec1 (talk | contribs) (put prototype into <source> tag)(diff) ← Previous revision | Latest revision (diff) | Newer revision → (diff)atoi is a function in the C programming language that converts a string into an integer numerical representation. atoi stands for ASCII to integer. It is included in the C standard library header file stdlib.h. It's prototype is as follows:
int '''atoi'''(const char *str);
The str argument is a string, represented by an array of characters, containing the characters of a signed integer number. The string must be null-terminated. When atoi encounters a string with no numerical sequence, it returns zero (0). If the string holds a valid sequence of digits that represents the number 0, it also returns a 0, making it impossible to tell from the return value alone whether the string holds a valid number or not. The newer function strtol does not have this deficiency.
Other problems of atoi are that it is not thread-safe and not async-cancel safe on some operating systems.
Variants of the atoi function, atol, atof, and atoll (the latter formerly known as atoq), are used to convert a string into a long, double, or long long type, respectively:
long atol(const char *str)double atof(const char *str)long long atoll(const char *str)(C99)
Standards conformance
The atoi, atof, and atol functions are a part of the ISO standard C library (C89), while the atoll function is added by C99.
However, because of the ambiguity in returning 0 and lack of thread-safety and async-cancel safety on some operating system, atoi is considered to be deprecated by strtol.
References
The Version 7 Unix Manual Pages © 1979 by Bell Telephone Laboratories, Incorporated.
The Version 1 Unix Manual page for atoi written by Ken Thompson (November 1971).