diff --git a/libc/src/stdio/scanf_core/CMakeLists.txt b/libc/src/stdio/scanf_core/CMakeLists.txt
index 3941d40a838c7..91cf5e2ada907 100644
--- a/libc/src/stdio/scanf_core/CMakeLists.txt
+++ b/libc/src/stdio/scanf_core/CMakeLists.txt
@@ -23,3 +23,38 @@ add_object_library(
     libc.src.__support.CPP.bitset
     libc.src.__support.CPP.string_view
 )
+
+if(NOT (TARGET libc.src.__support.File.file))
+  # Not all platforms have a file implementation. If file is unvailable,
+  # then we must skip all the parts that need file.
+  return()
+endif()
+
+add_object_library(
+  string_reader
+  SRCS
+    string_reader.cpp
+  HDRS
+    string_reader.h
+)
+
+add_object_library(
+  file_reader
+  SRCS
+    file_reader.cpp
+  HDRS
+    file_reader.h
+  DEPENDS
+    libc.src.__support.File.file
+)
+
+add_object_library(
+  reader
+  SRCS
+    reader.cpp
+  HDRS
+    reader.h
+  DEPENDS
+    .string_reader
+    .file_reader
+)
diff --git a/libc/src/stdio/scanf_core/file_reader.cpp b/libc/src/stdio/scanf_core/file_reader.cpp
new file mode 100644
index 0000000000000..f39c3b9ab8412
--- /dev/null
+++ b/libc/src/stdio/scanf_core/file_reader.cpp
@@ -0,0 +1,26 @@
+//===-- FILE Reader implementation for scanf --------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/stdio/scanf_core/file_reader.h"
+#include "src/__support/File/file.h"
+#include <stddef.h>
+
+namespace __llvm_libc {
+namespace scanf_core {
+
+char FileReader::get_char() {
+  char tiny_buff = 0;
+  if (file->read_unlocked(&tiny_buff, 1) != 1)
+    return 0;
+  return tiny_buff;
+}
+
+void FileReader::unget_char(char c) { file->ungetc_unlocked(c); }
+
+} // namespace scanf_core
+} // namespace __llvm_libc
diff --git a/libc/src/stdio/scanf_core/file_reader.h b/libc/src/stdio/scanf_core/file_reader.h
new file mode 100644
index 0000000000000..5e97eb604e66b
--- /dev/null
+++ b/libc/src/stdio/scanf_core/file_reader.h
@@ -0,0 +1,38 @@
+//===-- FILE Reader definition for scanf ------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_STDIO_SCANF_CORE_FILE_READER_H
+#define LLVM_LIBC_SRC_STDIO_SCANF_CORE_FILE_READER_H
+
+#include "src/__support/File/file.h"
+
+#include <stddef.h>
+#include <stdio.h>
+
+namespace __llvm_libc {
+namespace scanf_core {
+
+class FileReader {
+  __llvm_libc::File *file;
+
+public:
+  FileReader(::FILE *init_file) {
+    file = reinterpret_cast<__llvm_libc::File *>(init_file);
+    file->lock();
+  }
+
+  ~FileReader() { file->unlock(); }
+
+  char get_char();
+  void unget_char(char c);
+};
+
+} // namespace scanf_core
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_STDIO_SCANF_CORE_FILE_READER_H
diff --git a/libc/src/stdio/scanf_core/reader.cpp b/libc/src/stdio/scanf_core/reader.cpp
new file mode 100644
index 0000000000000..23dcbd405505d
--- /dev/null
+++ b/libc/src/stdio/scanf_core/reader.cpp
@@ -0,0 +1,35 @@
+//===-- Reader definition for scanf -----------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/stdio/scanf_core/reader.h"
+#include <stddef.h>
+
+namespace __llvm_libc {
+namespace scanf_core {
+
+char Reader::getc() {
+  if (reader_type == ReaderType::String) {
+    return string_reader->get_char();
+  } else {
+    return file_reader->get_char();
+  }
+}
+
+void Reader::ungetc(char c) {
+  if (reader_type == ReaderType::String) {
+    // The string reader ignores the char c passed to unget since it doesn't
+    // need to place anything back into a buffer, and modifying the source
+    // string would be dangerous.
+    return string_reader->unget_char();
+  } else {
+    return file_reader->unget_char(c);
+  }
+}
+
+} // namespace scanf_core
+} // namespace __llvm_libc
diff --git a/libc/src/stdio/scanf_core/reader.h b/libc/src/stdio/scanf_core/reader.h
new file mode 100644
index 0000000000000..4d6ed06c00e7c
--- /dev/null
+++ b/libc/src/stdio/scanf_core/reader.h
@@ -0,0 +1,49 @@
+//===-- Reader definition for scanf -----------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_STDIO_SCANF_CORE_READER_H
+#define LLVM_LIBC_SRC_STDIO_SCANF_CORE_READER_H
+
+#include "src/stdio/scanf_core/file_reader.h"
+#include "src/stdio/scanf_core/string_reader.h"
+#include <stddef.h>
+
+namespace __llvm_libc {
+namespace scanf_core {
+
+enum class ReaderType { String, File };
+
+class Reader final {
+  union {
+    StringReader *string_reader;
+    FileReader *file_reader;
+  };
+
+  const ReaderType reader_type;
+
+public:
+  Reader(StringReader *init_string_reader)
+      : string_reader(init_string_reader), reader_type(ReaderType::String) {}
+
+  Reader(FileReader *init_file_reader)
+      : file_reader(init_file_reader), reader_type(ReaderType::File) {}
+
+  // This returns the next character from the input and advances it by one
+  // character. When it hits the end of the string or file it returns '\0' to
+  // signal to stop parsing.
+  char getc();
+
+  // This moves the input back by one character, placing c into the buffer if
+  // this is a file reader, else c is ignored.
+  void ungetc(char c);
+};
+
+} // namespace scanf_core
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_STDIO_SCANF_CORE_READER_H
diff --git a/libc/src/stdio/scanf_core/string_reader.cpp b/libc/src/stdio/scanf_core/string_reader.cpp
new file mode 100644
index 0000000000000..1d728d2b9eb35
--- /dev/null
+++ b/libc/src/stdio/scanf_core/string_reader.cpp
@@ -0,0 +1,24 @@
+//===-- String Reader implementation for scanf ------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/stdio/scanf_core/string_reader.h"
+#include <stddef.h>
+
+namespace __llvm_libc {
+namespace scanf_core {
+
+char StringReader::get_char() {
+  char cur_char = string[cur_index];
+  ++cur_index;
+  return cur_char;
+}
+
+void StringReader::unget_char() { --cur_index; }
+
+} // namespace scanf_core
+} // namespace __llvm_libc
diff --git a/libc/src/stdio/scanf_core/string_reader.h b/libc/src/stdio/scanf_core/string_reader.h
new file mode 100644
index 0000000000000..35550b16c3214
--- /dev/null
+++ b/libc/src/stdio/scanf_core/string_reader.h
@@ -0,0 +1,33 @@
+//===-- String Reader definition for scanf ----------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_STDIO_SCANF_CORE_STRING_READER_H
+#define LLVM_LIBC_SRC_STDIO_SCANF_CORE_STRING_READER_H
+
+#include <stddef.h>
+
+namespace __llvm_libc {
+namespace scanf_core {
+
+class StringReader {
+  const char *string;
+  size_t cur_index = 0;
+
+public:
+  StringReader(const char *init_string) { string = init_string; }
+
+  ~StringReader() {}
+
+  char get_char();
+  void unget_char();
+};
+
+} // namespace scanf_core
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_STDIO_SCANF_CORE_STRING_READER_H
diff --git a/libc/test/src/stdio/scanf_core/CMakeLists.txt b/libc/test/src/stdio/scanf_core/CMakeLists.txt
index 3235a0e53e010..fa4878ae5b15f 100644
--- a/libc/test/src/stdio/scanf_core/CMakeLists.txt
+++ b/libc/test/src/stdio/scanf_core/CMakeLists.txt
@@ -12,3 +12,21 @@ add_libc_unittest(
     libc.src.__support.CPP.string_view
     libc.src.__support.arg_list
 )
+
+if(NOT (TARGET libc.src.__support.File.file))
+  # Not all platforms have a file implementation. If file is unvailable,
+  # then we must skip all the parts that need file.
+  return()
+endif()
+
+add_libc_unittest(
+  string_reader_test
+  SUITE
+    libc_stdio_unittests
+  SRCS
+    string_reader_test.cpp
+  DEPENDS
+    libc.src.stdio.scanf_core.reader
+    libc.src.stdio.scanf_core.string_reader
+    libc.src.__support.CPP.string_view
+)
diff --git a/libc/test/src/stdio/scanf_core/string_reader_test.cpp b/libc/test/src/stdio/scanf_core/string_reader_test.cpp
new file mode 100644
index 0000000000000..43e65cc1bab6e
--- /dev/null
+++ b/libc/test/src/stdio/scanf_core/string_reader_test.cpp
@@ -0,0 +1,66 @@
+//===-- Unittests for the scanf String Reader -----------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/__support/CPP/string_view.h"
+#include "src/stdio/scanf_core/reader.h"
+#include "src/stdio/scanf_core/string_reader.h"
+
+#include "utils/UnitTest/Test.h"
+
+TEST(LlvmLibcScanfStringReaderTest, Constructor) {
+  char str[10];
+  __llvm_libc::scanf_core::StringReader str_reader(str);
+  __llvm_libc::scanf_core::Reader reader(&str_reader);
+}
+
+TEST(LlvmLibcScanfStringReaderTest, SimpleRead) {
+  const char *str = "abc";
+  __llvm_libc::scanf_core::StringReader str_reader(str);
+  __llvm_libc::scanf_core::Reader reader(&str_reader);
+
+  for (size_t i = 0; i < sizeof(str); ++i) {
+    ASSERT_EQ(str[i], reader.getc());
+  }
+}
+
+TEST(LlvmLibcScanfStringReaderTest, ReadAndReverse) {
+  const char *str = "abcDEF123";
+  __llvm_libc::scanf_core::StringReader str_reader(str);
+  __llvm_libc::scanf_core::Reader reader(&str_reader);
+
+  for (size_t i = 0; i < 5; ++i) {
+    ASSERT_EQ(str[i], reader.getc());
+  }
+
+  // Move back by 3, cursor should now be on 2
+  reader.ungetc(str[4]);
+  reader.ungetc(str[3]);
+  reader.ungetc(str[2]);
+
+  for (size_t i = 2; i < 7; ++i) {
+    ASSERT_EQ(str[i], reader.getc());
+  }
+
+  // Move back by 2, cursor should now be on 5
+  reader.ungetc(str[6]);
+  reader.ungetc(str[5]);
+
+  for (size_t i = 5; i < 10; ++i) {
+    ASSERT_EQ(str[i], reader.getc());
+  }
+
+  // Move back by 10, which should be back to the start.
+  for (size_t i = 0; i < 10; ++i) {
+    reader.ungetc(str[9 - i]);
+  }
+
+  // Check the whole string.
+  for (size_t i = 0; i < sizeof(str); ++i) {
+    ASSERT_EQ(str[i], reader.getc());
+  }
+}