Parse URLs using C-Strings in C++

Question

I'm learning C++ for one of my CS classes, and for our first project I need to parse some URLs using c-strings (i.e. I can't use the C++ String class).

The only way I can think of approaching this is just iterating through (since it's a char[]) and using some switch statements. From someone who is more experienced in C++ - is there a better approach? Could you maybe point me to a good online resource? I haven't found one yet.

Answer 1

Weird that you're not allowed to use C++ language features i.e. C++ strings!

There are some C string functions available in the standard C library.

e.g.

strdup - duplicate a string
strtok - breaking a string into tokens. Beware - this modifies the original string.
strcpy - copying string
strstr - find string in string
strncpy - copy up to n bytes of string
etc

There is a good online reference here with a full list of available c string functions for searching and finding things.

http://www.cplusplus.com/reference/clibrary/cstring/

You can walk through strings by accessing them like an array if you need to.

e.g.

char* url="http://stackoverflow.com/questions/1370870/c-strings-in-c"
int len = strlen(url);
for (int i = 0; i < len; ++i){
  std::cout << url[i];
}
std::cout << endl;

As for actually how to do the parsing, you'll have to work that out on your own. It is an assignment after all.

Answer 2

There are a number of C standard library functions that can help you.

First, look at the C standard library function strtok. This allows you to retrieve parts of a C string separated by certain delimiters. For example, you could tokenize with the delimiter / to get the protocol, domain, and then the file path. You could tokenize the domain with delimiter . to get the subdomain(s), second level domain, and top level domain. Etc.

It's not nearly as powerful as a regular expression parser, which is what you would really want for parsing URLs, but it works on C strings, is part of the C standard library and is probably OK to use in your assignment.

Other C standard library functions that may help:

• strstr() Extracts substrings just like std::string::substr()
• strspn(), strchr() and strpbrk() Find a character or characters in a string, similar to std::string::find_first_of(), etc.

Edit: A reminder that the proper way to use these functions in C++ is to include <cstring> and use them in the std:: namespace, e.g. std::strtok().