Scan Functions

For the scan functions, literal text in a format string must match the next characters to scan in the input text. White space in a format string must match the longest possible sequence of the next zero or more white-space characters in the input. Except for the scan conversion specifier %n (which consumes no input), each scan conversion specification determines a pattern that one or more of the next characters in the input must match. And except for the scan conversion specifiers c, n, and [, every match begins by skipping any white space characters in the input.

A scan function returns when:

• it reaches the terminating null in the format string
• it cannot obtain additional input characters to scan (input failure)
• a conversion fails (matching failure)

A scan function returns EOF if an input failure occurs before any conversion. Otherwise it returns the number of converted values stored. If one or more characters form a valid prefix but the conversion fails, the valid prefix is consumed before the scan function returns. Thus:

    scanf(“%i”, &i)       consumes 0X from field 0XZ
    scanf(“%f”, &f)       consumes 3.2E from field 3.2EZ

A scan conversion specification typically converts the matched input characters to a corresponding encoded value. The next argument value must be the address of an object. The conversion converts the encoded representation (as necessary) and stores its value in the object. A scan conversion specification has the format shown in the diagram.

Following the percent character (%) in the format string, you can write an asterisk (*) to indicate that the conversion should not store the converted value in an object.

Following any *, you can write a nonzero field width that specifies the maximum number of input characters to match for the conversion (not counting any white space that the pattern can first skip).