diff --git a/lib/std/core/string.c3 b/lib/std/core/string.c3
index fa654aead..6f1a287ef 100644
--- a/lib/std/core/string.c3
+++ b/lib/std/core/string.c3
@@ -75,7 +75,8 @@ fn void String.chop(String this, usize new_size)
 fn char[] String.str(String str)
 {
 	StringData* data = (StringData*)str;
-	return data.chars[0..data.len - 1];
+	if (!data) return char[] {};
+	return data.chars[:data.len];
 }
 
 fn void String.append_utf32(String* str, Char32[] chars)
@@ -173,6 +174,11 @@ fn ZString String.copy_zstr(String* str, Allocator allocator = { null, null })
 	return (ZString)zstr;
 }
 
+fn char[] String.copy_str(String* str, Allocator allocator = { null, null })
+{
+	return str.copy_zstr(allocator)[:str.len()];
+}
+
 fn bool String.equals(String str, String other_string)
 {
 	StringData *str1 = str.data();
diff --git a/lib/std/io.c3 b/lib/std/io.c3
index 8e7a14111..e2511aa9d 100644
--- a/lib/std/io.c3
+++ b/lib/std/io.c3
@@ -166,6 +166,11 @@ fn usize! File.println(File* file, char[] string)
     return len + 1;
 }
 
+fn File stdout()
+{
+	return { libc::stdout() };
+}
+
 /*
 
 
diff --git a/lib/std/io_printf.c3 b/lib/std/io_printf.c3
index ac9ce4938..9151c94c0 100644
--- a/lib/std/io_printf.c3
+++ b/lib/std/io_printf.c3
@@ -28,14 +28,14 @@ bitstruct PrintFlags : uint
 struct PrintParam
 {
 	OutputFn outfn;
-	char[] buffer;
+	void* buffer;
 	PrintFlags flags;
 	uint width;
 	uint prec;
 	usize idx;
 }
 
-define OutputFn = fn void!(char c, char[] buffer, usize buffer_idx);
+define OutputFn = fn void!(char c, void* buffer, usize buffer_idx);
 
 fn void! PrintParam.out(PrintParam* param, char c)
 {
@@ -207,15 +207,27 @@ private fn void! out_buffer_fn(char c, char[] buffer, usize buffer_idx)
 	buffer[buffer_idx] = c;
 }
 
-private fn void! out_null_fn(char c @unused, char[] buffer @unused, usize idx @unused)
+private fn void! out_null_fn(char c @unused, void* data @unused, usize idx @unused)
 {
 }
 
-private fn void! out_putchar_fn(char c, char[] buffer @unused, usize idx @unused)
+private fn void! out_putchar_fn(char c, void* data @unused, usize idx @unused)
 {
 	libc::putchar(c);
 }
 
+private fn void! out_fputchar_fn(char c, void* data, usize idx @unused)
+{
+	File* f = data;
+	f.putc(c)?;
+}
+
+private fn void! out_string_append_fn(char c, void* data, usize idx @unused)
+{
+	String* s = data;
+	s.append_char(c);
+}
+
 private fn void! PrintParam.out_reverse(PrintParam* param, char[] buf)
 {
 	usize buffer_start_idx = param.idx;
@@ -702,7 +714,17 @@ private fn NtoaType int_from_variant(variant arg, bool *is_neg)
 
 fn usize! printf(char[] format, args...) @maydiscard
 {
-  return vsnprintf(&out_putchar_fn, " ", format, args);
+  return vsnprintf(&out_putchar_fn, null, format, args);
+}
+
+fn usize! String.printf(String* str, char[] format, args...) @maydiscard
+{
+	return vsnprintf(&out_string_append_fn, str, format, args);
+}
+
+fn usize! fprintf(File file, char[] format, args...) @maydiscard
+{
+  return vsnprintf(&out_putchar_fn, &file, format, args);
 }
 
 private fn void! PrintParam.left_adjust(PrintParam* param, usize len)
@@ -737,14 +759,14 @@ private fn void! out_substr(PrintParam* param, char[] str)
 	return param.left_adjust(l);
 }
 
-private fn usize! vsnprintf(OutputFn out, char[] buffer, char[] format, variant[] variants)
+private fn usize! vsnprintf(OutputFn out, void* data, char[] format, variant[] variants)
 {
-	if (!buffer)
+	if (!out)
 	{
 		// use null output function
 		out = &out_null_fn;
 	}
-	PrintParam param = { .outfn = out, .buffer = buffer };
+	PrintParam param = { .outfn = out, .buffer = data };
 	usize format_len = format.len;
 	usize variant_index = 0;
 	for (usize i = 0; i < format_len; i++)
diff --git a/resources/examples/contextfree/boolerr.c3 b/resources/examples/contextfree/boolerr.c3
index d6824b38b..3fbf2181c 100644
--- a/resources/examples/contextfree/boolerr.c3
+++ b/resources/examples/contextfree/boolerr.c3
@@ -3,20 +3,26 @@ import libc;
 import std::io;
 
 struct Doc { Head *head; }
-struct Head { char[]* title; }
+struct Head { String* title; }
 
 struct Summary
 {
-	char[]* title;
+	String* title;
 	bool ok;
 }
 
-fn void Summary.print(Summary *s, CFile out)
+private struct StringData
 {
-	// We don't have a native fprintf in C3 yet, so use libc,
-	// which is not all that nice for the strings but...
-	char[] title = s.title ? *s.title : "missing";
-	libc::fprintf(out, "Summary({ .title = %.*s, .ok = %s})", (int)title.len, title.ptr, s.ok ? "true" : "false");
+	Allocator allocator;
+	usize len;
+	usize capacity;
+	char[*] chars;
+}
+
+fn void Summary.print(Summary *s, File out)
+{
+	char[] title = s.title ? s.title.str() : "missing";
+	io::fprintf(out, "Summary({ .title = %s, .ok = %s})", title, s.ok);
 }
 
 fn bool contains(char[] haystack, char[] needle)
@@ -36,7 +42,7 @@ fn bool contains(char[] haystack, char[] needle)
 	return false;
 }
 
-macro dupe(value)
+macro @dupe(value)
 {
 	$typeof(&value) temp = mem::alloc_checked($sizeof(value))?;
 	*temp = value;
@@ -52,13 +58,11 @@ fn Doc! readDoc(char[] url)
 {
 	if (contains(url, "fail")) return ReadError.BAD_READ!;
 	if (contains(url, "head-missing")) return { .head = null };
-	if (contains(url, "title-missing")) return { dupe(Head { .title = null })? };
-	if (contains(url, "title-empty")) return { dupe(Head { .title = dupe((char[])"")? })? };
-	// Not particularly elegant due to missing string functions.
-	int len = libc::snprintf(null, 0, "Title of %.*s", (int)url.len, url.ptr);
-	char* str = mem::alloc_checked(len + 1)?;
-	libc::snprintf(str, len + 1, "Title of %.*s", (int)url.len, url.ptr);
-	return { dupe(Head { .title = dupe(str[..len - 1])? })? };
+	if (contains(url, "title-missing")) return { @dupe(Head { .title = null }) };
+	if (contains(url, "title-empty")) return { @dupe(Head { .title = @dupe((String)null) }) };
+	String str;
+	str.printf("Title of %s", url);
+	return { @dupe(Head { .title = @dupe(str) }) };
 }
 
 fn Summary buildSummary(Doc doc)
@@ -93,9 +97,9 @@ fault TitleResult
 fn bool! isTitleNonEmpty(Doc doc)
 {
 	if (!doc.head) return TitleResult.TITLE_MISSING!;
-	char[]* head = doc.head.title;
+	String* head = doc.head.title;
 	if (!head) return TitleResult.TITLE_MISSING!;
-	return (*head).len > 0;
+	return head.len() > 0;
 }
 
 
@@ -123,13 +127,11 @@ fn void main()
             io::printf(`Checking "https://%s/":` "\n", url);
             Summary summary = readAndBuildSummary(url);
             io::printf("  Summary: ");
-            summary.print(libc::stdout());
+            summary.print(io::stdout());
             io::println("");
-            char[] title_sure = summary.title ? *summary.title : "";
+            char[] title_sure = summary.title ? summary.title.str() : "";
             io::printf("  Title: %s\n", title_sure);
             bool! has_title = readWhetherTitleNonEmpty(url);
-            // This looks a bit less than elegant, but as you see it's mostly due to having to
-            // use printf here.
             io::printf("  Has title: %s vs %s\n", bool_to_string(has_title) ?? catch(has_title).nameof, has_title ?? false);
         };
         allocator.reset();