Lecture 15 – Mar 6th, 2020

Setup

1. Log in to clyde.
2. Create a directory and cd into it.
3. Copy ~steve/ex/ptr.c into the directory.

Task

1. Implement

   size_t simple_strlen(char const *str);
   

   to return the length of the string argument str, not counting the final 0 byte.

   You will want to loop over each character in the string and check if it is 0 or not (note that 0 and '0' are very different). You can do this by checking if str[length] is 0 and if so, return length. If it isn’t 0, increment length by one.

   Alternatively, you can use pointer arithmetic and loop while *str is not 0. In the body of the loop, increment both length and str.

2. The environment variables are available in a variable in unistd.h.

   extern char **environ;
   

   (Remember that extern just means it’s defined somewhere else.)

   environ is a pointer to an array of strings and it ends with a NULL pointer. That is, environ[0] is the 0th environment variable, environ[1] is the 1st, and so on. If there are n environment variables, then environ[n] is NULL. The number of environment variables isn’t stored for you.

   Print out how many environment variables.

   Your final output should be something like this (but you may have a different number of environment variables).

   $ ./ptr foo 'bar baz'
   Arg 0 [./ptr] has length 5
   Arg 1 [foo] has length 3
   Arg 2 [bar baz] has length 7
   There are 53 environment variables