% 64 [^ specifier in C

Question

sscanf(line, "%d %64[^\n", &seconds, message); 

has a value of % 64 [^ - up to 64 characters? Should it work with the GNU C compiler?

Answer 1

This means that "read no more than 64 characters or stop when a new line is reached, whichever comes first." It is specified by the standard, so all standard libraries must support it.

C11 7.21.6.2

[ Corresponds to a nonempty sequence of characters from the set of expected characters (scan). [...] The conversion specifier includes all subsequent characters in the format string, up to the appropriate right bracket (]).

The characters between the brackets (scan list) constitute a scanset if the character after the left bracket is not bypassed (^), in which case the scan contains all the characters that are not displayed in the scan list between the envelope and the right bracket.

As noted in the comments, matching may be required ] to delimit the scan list. The s not required .