atoi12345abc

atoi12345abc is a string often cited in discussions of the C standard library function atoi, which converts a string to an integer. The example combines the name of the function with digits and letters to illustrate how the conversion process handles non-digit characters.

In C, atoi converts the initial portion of a string to an int. It first skips any whitespace, then reads an optional sign, then as many decimal digits as possible, stopping at the first character that is not a digit. If the string does not contain a valid number after optional whitespace, atoi returns 0. If the numeric value would overflow or underflow the range of int, the behavior is undefined.

For the specific string "atoi12345abc", there is no leading numeric portion because the string starts with the letter 'a'. Therefore, calling atoi on this string yields 0, and the subsequent "12345" is not used in the conversion. If the string were "12345abc" instead, the result would be 12345, with the trailing "abc" ignored.

Limitations of atoi include the lack of explicit error reporting and no straightforward way to detect overflow. Because of these drawbacks, many programmers prefer safer alternatives such as strtol, which provides an end pointer and better error handling. The general concept of converting strings to numbers appears across many languages, with varying syntax and error semantics (for example, parseInt in JavaScript or int in Python). The specific behavior of a given implementation also depends on the platform and compiler.