added optional argument flag parsing

k&r/04-funcs-and-prog-struct/04-find/04-find.c

@@ -5,21 +5,52 @@
 
 int find(char *pattern);
 
+#define ARG_FLAGS X('n', lineno) X('x', except)
+
 /* find pattern given by first arg in lines and print them
- * compile with 04-find-no-overflow.c or 04-find-opt.c */
+ * takes optional flags 
+ * -x : print all except matching
+ * -n : print line numbers */
 int main(int argc, char *argv[])
 {
-    /* verify arg is given */
-    if (argc < 2) {
-        printf("error: excpected pattern\n");
+    int i;
+    char c;
+
+    /* declare flag variables  */
+#define X(c, flag_var) int flag_var = 0;
+    ARG_FLAGS
+#undef X
+    char **parg = argv;
+    /* parse flag arguments */
+    for (i = 1; *++parg; ) {
+        if (**parg != '-' || !(*parg)[1]) {
+            argv[i++] = *parg;
+            continue;
+        }
+        while (c = *++parg[0])
+            switch (c) {
+        #define X(C, flag_var) case C: flag_var = 1; break;
+            ARG_FLAGS
+        #undef X
+            default: 
+                printf("error: illegal option -%c\n", c);
+                argc = 0;
+                break;
+            }
+        --argc;
+    }
+
+    if (argc != 2) {
+        printf("usage: find ");
+    #define X(c, _) printf("[-%c] ", c);
+        ARG_FLAGS
+    #undef X
+        printf("pattern\n");
         return -1;
     }
 
     char *pattern = argv[1];
-
     /* verify pattern */
-    char c;
-    int i;
     for (i = 0; (c = pattern[i]) != '\0'; i++)
         if (c == '\n') {
             printf("error: newline in pattern\n");
@@ -27,6 +58,5 @@ int main(int argc, char *argv[])
         }
 
     int found = find(pattern);
-    printf("found = %d\n", found);
     return found;
 }