llvm/lib/Support/FileUtilities.cpp

//===- Support/FileUtilities.cpp - File System Utilities ------------------===//
// 
//                     The LLVM Compiler Infrastructure
//
// This file was developed by the LLVM research group and is distributed under
// the University of Illinois Open Source License. See LICENSE.TXT for details.
// 
//===----------------------------------------------------------------------===//
//
// This file implements a family of utility functions which are useful for doing
// various things with files.
//
//===----------------------------------------------------------------------===//

#include "llvm/Support/FileUtilities.h"
#include "llvm/System/Path.h"
#include <fstream>
#include <iostream>

using namespace llvm;

/// DiffFiles - Compare the two files specified, returning true if they are
/// different or if there is a file error.  If you specify a string to fill in
/// for the error option, it will set the string to an error message if an error
/// occurs, allowing the caller to distinguish between a failed diff and a file
/// system error.
///
bool llvm::DiffFiles(const std::string &FileA, const std::string &FileB,
                     std::string *Error) {
  std::ios::openmode io_mode = std::ios::in | std::ios::binary;
  std::ifstream FileAStream(FileA.c_str(), io_mode);
  if (!FileAStream) {
    if (Error) *Error = "Couldn't open file '" + FileA + "'";
    return true;
  }

  std::ifstream FileBStream(FileB.c_str(), io_mode);
  if (!FileBStream) {
    if (Error) *Error = "Couldn't open file '" + FileB + "'";
    return true;
  }

  // Compare the two files...
  int C1, C2;
  do {
    C1 = FileAStream.get();
    C2 = FileBStream.get();
    if (C1 != C2) return true;
  } while (C1 != EOF);

  return false;
}

/// MoveFileOverIfUpdated - If the file specified by New is different than Old,
/// or if Old does not exist, move the New file over the Old file.  Otherwise,
/// remove the New file.
///
void llvm::MoveFileOverIfUpdated(const std::string &New,
                                 const std::string &Old) {
  if (DiffFiles(New, Old)) {
    if (std::rename(New.c_str(), Old.c_str()))
      std::cerr << "Error renaming '" << New << "' to '" << Old << "'!\n";
  } else {
    std::remove(New.c_str());
  }  
}