The C++ equivalent of C's format string [closed]

Question

I have a C program that reads from keyboard, like this:

scanf("%*[ \t\n]\"%[^A-Za-z]%[^\"]\"", ps1, ps2);

For a better understanding of what this instruction does, let's split the format string as follows:

%*[ \t\n]\" => read all spaces, tabs and newlines ([ \t\n]) but not store them in any variable (hence the '*'), and will keep reading until encounter a double quote (\"), however the double quote is not input.

Once scanf() has found the double quote, reads all caracters that are not letters into ps1. This is accomplished with...

%[^A-Za-z] => input anything not an uppercase letter 'A' through 'Z' and lowercase letter 'a' through 'z'.

%[^\"]\" => read all remaining characters up to, but not including a double quote into ps2 ([^\"]) and the string must end with a double quote (\"), however the double quote is not input.

Can someone show me how to do the same thing in C++

Thank you

Answer 1

C++ supports the scanf function. There is no simple alternative, especially if you want to replicate the exact semantics of scanf() with all the quirks.

Note however that your code has several issues:

• You do not pass the maximum number of characters to read into ps1 and ps2. Any sufficiently input sequence will cause a buffer overflow with dire consequences.

• You could simplify the first format %*[ \t\n] with just a space in the format string. This would also allow for the case where no whitespace characters are present. As currently written, scanf() would fail and return 0 if no whitspace characters are present before the ".

• Similarly, if no non letters or if no other characters follow before the second ", scanf would return a short count of 0 or 1 and leave one or both destination array in an indeterminate state.

For all these reasons, it would be much safer and predictable in C to first read a line of input with fgets() and use sscanf() or parse the line by hand.

In C++, you definitely want to use the std::regex package defined in <regex.h>.