C 语言：scanf 和 sscanf 表达式

Question

I've encountered a expressions that go something like this inside scanf and sscanf arguments:

sscanf(buffer, "%d,%100[^,]%*c%f", destination_pointer)

or

scanf("\n%99s", destination);

What is the correct way of interpreting these? I know what things like "%s %c %d" are, and also that the %100 or generally "%number" is the size of the input to be read. But what about the rest? All I can find are basic examples, nothing near this complex. Is there any reference guide?

Answer 1

What is the correct way to interpreted these?

sscanf(buffer, "%d,%100[^,]%*c%f", destinantion_pointer)

Is an invalid call. There are 3 conversion specifiers that need an argument - %d , %[] , %f . That means exactly 3 arguments after formatting string are needed, but only one destinantion_pointer is provided.

• %d - ignore any whitespace characters, read an int in base 10
• , - read a comma
• %100[^,] - read maximum number of 100 characters that are not a comma. Maximum up to 101 bytes (100 characters + null byte) are stored in destination buffer.
  • %[set] - reads characters in the set
  • %[^set] - reads characters that are not in the set
• %*c - ignore one character (a comma, because %100[^,] reads up until a comma, or the string has ended, which would make scanf return here). Note - ignoring the result of conversion with * makes scanf not increment the return value in the case reading was successful.
• %f - ignore any whitespace characters, read a float (in any format - decimal, scientific or hexadecimal)

scanf("\\n%99s", destinantion);

• \\n - read (and ignore) any number of whitespace characters (whitespace, means anything for that isspace() returns nonzero, so either space, form feed, line feed, carriage return, tab or vertical tab)
• %99s - ignore any leading whitespace characters ( \\n in front of it is useless...), then read up to 99 characters that are not whitespaces (the resulting buffer has to be at least 100 bytes long).