From f6123ac9f1044e4e7ef03145ee5ccda5fd3339e4 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ciro=20Santilli=20=E5=85=AD=E5=9B=9B=E4=BA=8B=E4=BB=B6=20?=
 =?UTF-8?q?=E6=B3=95=E8=BD=AE=E5=8A=9F?= <ciro.santilli@gmail.com>
Date: Fri, 18 Oct 2019 00:00:01 +0000
Subject: [PATCH] c++: file_read_write

---
 README.adoc                      |  2 ++
 userland/cpp/file_write_read.cpp | 46 ++++++++++++++++++++++++++++++++
 2 files changed, 48 insertions(+)
 create mode 100644 userland/cpp/file_write_read.cpp

diff --git a/README.adoc b/README.adoc
index 1d3af70..51e7864 100644
--- a/README.adoc
+++ b/README.adoc
@@ -13540,6 +13540,8 @@ Programs under link:userland/cpp/[] are examples of https://en.wikipedia.org/wik
 ** link:userland/cpp/template.cpp[]: basic example
 ** link:userland/cpp/template_class_with_static_member.cpp[]: https://stackoverflow.com/questions/3229883/static-member-initialization-in-a-class-template
 ** link:userland/cpp/if_constexpr.cpp[]: C++17 `if constexpr`
+* fstream
+** link:userland/cpp/file_write_read.cpp[]
 
 [[cpp-multithreading]]
 ==== C++ multithreading
diff --git a/userland/cpp/file_write_read.cpp b/userland/cpp/file_write_read.cpp
new file mode 100644
index 0000000..b67733e
--- /dev/null
+++ b/userland/cpp/file_write_read.cpp
@@ -0,0 +1,46 @@
+/* https://cirosantilli.com/linux-kernel-module-cheat#cpp */
+
+#include <lkmc.h>
+
+#include <cassert>
+#include <fstream>
+#include <sstream>
+
+// https://stackoverflow.com/questions/116038/what-is-the-best-way-to-read-an-entire-file-into-a-stdstring-in-c
+// https://stackoverflow.com/questions/2602013/read-whole-ascii-file-into-c-stdstring
+std::string read_file(const std::string& path) {
+    std::ifstream ifs(path);
+    assert(ifs.is_open());
+    std::stringstream sstr;
+    sstr << ifs.rdbuf();
+    return sstr.str();
+}
+
+int main(void) {
+    std::string path = LKMC_TMP_FILE;
+    std::string data = "asdf\nqwer\n";
+
+    // Write entire string to file at once.
+    {
+        std::ofstream ofs(path);
+        assert(ofs.is_open());
+        ofs << data;
+        ofs.close();
+    }
+
+    // Read entire file into string.
+    std::string read_output = read_file(path);
+    assert(read_output == data);
+
+    // Append to a file.
+    {
+        std::string append_data = "zxcv\n";
+        std::ofstream ofs(path, std::ios::app);
+        assert(ofs.is_open());
+        ofs << append_data;
+        ofs.close();
+        assert(read_file(path) == data + append_data);
+    }
+
+    return EXIT_SUCCESS;
+}