Question

Yo!

I’m trying to copy a few chars from a char[] to a char*. I just want the chars from index 6 to (message length – 9).

Maybe the code example will explain my problem more:

char buffer[512] = 'GET /testfile.htm HTTP/1.0'; char* filename; // I want *filename to hold only '/testfile.htm'  msgLen = recv(connecting_socket, buffer, 512, 0); strncpy(filename, buffer+5, msgLen-9); 

Any response would help alot!

Answer 1

I assume you meant…

strncpy(filename, buffer+5, msgLen-9); 

The problem is you haven’t allocated any memory to hold the characters you’re copying. ‘filename’ is a pointer, but it doesn’t point at anything.

Either just declare

char filename[512]; 

or malloc some memory for the new name (and don’t forget to free() it…)

There are a few problems with the use of strncpy() in your code.

• buffer+5 points to the sixth character in string (the ‘T’), while you said you wanted the backslash.
• The last parameter is the maximum number of bytes to copy, so should probably be msglen-13.
• strncpy() won’t null terminate the copied string, so you need to do that manually.

• Also, from a readabilty perspective, I prefer

  strncpy(filename, &buffer[4], msgLen-(9 + 4));

&buffer[5] is the address of the character at the fifth position in the array. That’s a personal thing, though.

Also, worth pointing out that the result of ‘recv’ could be one byte or 512 bytes. It won’t just read a line. You should really loop calling recv until you have a complete line to work with.