* create basic strtok

* add test and expected output

src/string/src/lib.rs

@@ -323,8 +323,37 @@ pub unsafe extern "C" fn strstr(s1: *const c_char, s2: *const c_char) -> *mut c_
 }
 
 #[no_mangle]
-pub extern "C" fn strtok(s1: *mut c_char, s2: *const c_char) -> *mut c_char {
-    unimplemented!();
+pub extern "C" fn strtok(s1: *mut c_char, delimiter: *const c_char) -> *mut c_char {
+    // Loosely based on GLIBC implementation
+    unsafe {
+        static mut HAYSTACK: *mut c_char = ptr::null_mut();
+        if !s1.is_null() {
+            HAYSTACK = s1;
+        } else if HAYSTACK.is_null() {
+            return ptr::null_mut();
+        }
+
+        // Skip past any extra delimiter left over from previous call
+        HAYSTACK = HAYSTACK.add(strspn(HAYSTACK, delimiter));
+        if *HAYSTACK == 0 {
+            HAYSTACK = ptr::null_mut();
+            return ptr::null_mut();
+        }
+
+        // Build token by injecting null byte into delimiter
+        let token = HAYSTACK;
+        HAYSTACK = strpbrk(token, delimiter);
+        if !HAYSTACK.is_null() {
+            HAYSTACK.write(0 as c_char);
+            HAYSTACK = HAYSTACK.add(1);
+        } else {
+            HAYSTACK = ptr::null_mut();
+        }
+
+        return token;
+    }
+
+    ptr::null_mut()
 }
 
 #[no_mangle]