feat(string): complete string.h + strdup/memccpy

src/string/strchr.c

@@ -0,0 +1,52 @@
+#ifdef HAVE_CONFIG_H
+#include <config.h>
+#endif
+
+#include <string.h>
+
+/*
+ * Return a pointer to the first occurrence of c (converted to char) in s,
+ * or NULL when absent. The terminating NUL is part of the string, so
+ * strchr(s, '\0') returns a pointer to it.
+ */
+char *
+strchr(const char *s, int c) // NOLINT(bugprone-easily-swappable-parameters)
+{
+    const char cc = (char)c;
+
+    for (;; s++)
+    {
+        if (*s == cc)
+        {
+            return (char *)s;
+        }
+        if (*s == '\0')
+        {
+            return NULL;
+        }
+    }
+}
+
+/*
+ * Return a pointer to the last occurrence of c (converted to char) in s, or
+ * NULL when absent. The terminating NUL is part of the string, so
+ * strrchr(s, '\0') returns a pointer to it.
+ */
+char *
+strrchr(const char *s, int c) // NOLINT(bugprone-easily-swappable-parameters)
+{
+    const char cc = (char)c;
+    const char *last = NULL;
+
+    for (;; s++)
+    {
+        if (*s == cc)
+        {
+            last = s;
+        }
+        if (*s == '\0')
+        {
+            return (char *)last;
+        }
+    }
+}