feat: (cstr) strisblank

lib/cstr.c

@@ -140,3 +140,25 @@ strupcase (char *str)
             str++;
         }
 }
+
+/**
+ * check if a string only consists of whitespace characters.
+ *
+ * @param   str: the string to check
+ *
+ * @return  true if the string only consists of whitespace characters, or false
+ *          if other characters are present. false in case of error.
+ *
+ * @errno   EINVAL: `str` is a null pointer
+ */
+bool
+strisblank (const char *str)
+{
+    if (str == NULL) return errno = EINVAL, false;
+
+    while (*str)
+        if (!isspace (*str++))
+            return false;
+
+    return true;
+}

lib/inc/cstr.h

@@ -1,6 +1,7 @@
 #ifndef CUTILS_CSTR_H_
 #define CUTILS_CSTR_H_
 
+#include <stdbool.h>
 #include <stddef.h>
 #include <sys/types.h>
 
@@ -10,5 +11,6 @@ ssize_t strtrimr (char *str); /* trim whitespace of a cstring on the right (end
 ssize_t strcount (const char *str, char c); /* count number of occurances of a character within a string */
 void strdowncase (char *str); /* transform all uppercase letters of a string into lowercase letters */
 void strupcase (char *str); /* transform all lowercase letters of a string into uppercase letters */
+bool strisblank (const char *str); /* check if a string only consists of whitespace characters */
 
 #endif // CUTILS_CSTR_H_

test/main.c

@@ -42,6 +42,11 @@ test_cstr (void)
     test_add (&group, test_assert (!strcmp (s4, "hello, world!\n")), "strdowncase");
     test_add (&group, test_assert (!strcmp (s5, "HELLO, WORLD!\n")), "strupcase");
     
+    char *s6 = "    x    ";
+    char *s7 = " \r\n\t\v\f";
+    test_add (&group, test_assert (!strisblank (s6)), "strisblank false");
+    test_add (&group, test_assert (strisblank (s7)), "strisblank true");
+
     return test_group_get_results (&group);
 }