liblinux++

commit e73acf0554f059c01739e12aa2a18301943a3d6b
parent a962c85ccf6076e754363a6ea207ef20e3172b6a
Author: Henry Wilson <henry@henryandlizzy.uk>
Date:   Fri, 26 Dec 2025 20:03:31 +0000

writer: demo equivalent of std::ostringstream

Diffstat:
M
Tupfile
 | 
2
+-
M
linux.hpp
 | 
21
+++++++++++++++++++--
A
writer.cpp
 | 
81
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

3 files changed, 101 insertions(+), 3 deletions(-)
diff --git a/Tupfile b/Tupfile
@@ -1,4 +1,4 @@
-CXXFLAGS = -g -Os -fno-exceptions -fno-asynchronous-unwind-tables -fno-builtin -fno-pic -fno-pie -fno-stack-protector -fdiagnostics-color=always
+CXXFLAGS = -g -Os -fno-exceptions -fno-rtti -fno-asynchronous-unwind-tables -fno-builtin -fno-pic -fno-pie -fno-stack-protector -fdiagnostics-color=always
 LDFLAGS = --gc-sections
 
 : foreach *.cpp |> clang++ --target=aarch64 $(CXXFLAGS) -c -o %o %f |> obj/%B.aarch64.o {objs-aarch64}
diff --git a/linux.hpp b/linux.hpp
@@ -46,7 +46,7 @@ struct span
 {
 	span() = default;
 	inline span(T* p, size_t n)
-	: data{p}
+	: ptr{p}
 	, len{n}
 	{}
 
@@ -54,8 +54,25 @@ struct span
 	inline span(T (&arr)[N])
 	: span{arr, N}
 	{}
+
+	T* data() const noexcept
+	{
+		return ptr;
+	}
+	size_t size() const noexcept
+	{
+		return len;
+	}
+	T* begin() const noexcept
+	{
+		return data();
+	}
+	T* end() const noexcept
+	{
+		return begin() + size();
+	}
 private:
-	T* data = nullptr;
+	T* ptr = nullptr;
 	size_t len = 0;
 };
 
diff --git a/writer.cpp b/writer.cpp
@@ -0,0 +1,81 @@
+#include "linux.hpp"
+
+struct writer
+{
+	virtual void write(span<char const>) = 0;
+protected:
+	~writer() = default;
+};
+
+struct fd_writer : writer
+{
+	fd_writer(file f) : out{f} {}
+
+	void write(span<char const> data) override
+	{
+		if (*::write(out, data) != data.size())
+			__builtin_trap();
+	}
+private:
+	file out;
+};
+
+template <typename T>
+struct vector
+{
+	void push_back(T c)
+	{
+		if (used * sizeof(T) >= capacity)
+		{
+			size_t const old_cap = capacity;
+			size_t const new_cap = capacity ? capacity * 2 : 0x1000;
+			T* new_buf = (T*)*mmap(nullptr, new_cap, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_PRIVATE, {}, 0);
+			for (size_t i = 0; i < used; ++i)
+				new_buf[i] = buf[i];
+			capacity = new_cap;
+			if (buf)
+				*munmap(buf, old_cap);
+			buf = new_buf;
+		}
+
+		buf[used++] = c;
+	}
+
+	T const* data() const { return buf; }
+	T* data() { return buf; }
+	size_t size() const { return used; }
+private:
+	T* buf = nullptr;
+	size_t capacity = 0, used = 0;
+};
+
+struct buf_writer : writer
+{
+	buf_writer() noexcept = default;
+
+	void write(span<char const> data) override
+	{
+		for (char c : data)
+			buffer.push_back(c);
+	}
+	span<char const> get() const noexcept
+	{
+		return {buffer.data(), buffer.size()};
+	}
+private:
+	vector<char> buffer;
+};
+
+int main()
+{
+	buf_writer x;
+	writer* w = &x;
+	for (int i = 0; i < 240; ++i)
+	{
+		w->write("Hello, ");
+		w->write("World! Wow what a lovely day!\n");
+	}
+	fd_writer cout{stdout};
+	w = &cout;
+	w->write(x.get());
+}