strchr(3), strchrnul(3), strrchr(3)

cstdlib/string.c

@@ -1,3 +1,39 @@
+char *
+strchr(const char *s, int c){
+	char *r;
+
+	for(r = s; ; ++r){
+		if(*r == c)
+			return r;
+		if(*r == '\0')
+			return NULL;
+	}
+}
+
+char *
+strrchr(const char *s, int c){
+	char *r;
+	char *p;
+
+	for(p = s, r = NULL; ; ++p){
+		if(*p == c)
+			r = p;
+		if(*p == '\0')
+			break;
+	}
+
+	return r;
+}
+
+char *
+strchrnul(const char *s, int c){
+	char *r;
+
+	for(r = s; ; ++r)
+		if(*r == c || r == '\0')
+			return r;
+}
+
 size_t
 strlen(const char *s){
 	size_t r;

cstdlib/string.h

@@ -1,5 +1,8 @@
 #ifndef _STRING_H
 #	define _STRING_H
-size_t strlen(const char *s);
-size_t strnlen(const char *s, size_t maxlen);
+char *   strchr(const char *s, int c);
+char *  strrchr(const char *s, int c);
+char *strchrnul(const char *s, int c);
+size_t   strlen(const char *s);
+size_t  strnlen(const char *s, size_t maxlen);
 #endif /* ifndef _STRING_H */