从几个地方提取信息…这应该是最快最好的方法:

#include <filesystem>
#include <fstream>
#include <string>

//Returns true if successful.
bool readInFile(std::string pathString)
{
  //Make sure the file exists and is an actual file.
  if (!std::filesystem::is_regular_file(pathString))
  {
    return false;
  }
  //Convert relative path to absolute path.
  pathString = std::filesystem::weakly_canonical(pathString);
  //Open the file for reading (binary is fastest).
  std::wifstream in(pathString, std::ios::binary);
  //Make sure the file opened.
  if (!in)
  {
    return false;
  }
  //Wide string to store the file's contents.
  std::wstring fileContents;
  //Jump to the end of the file to determine the file size.
  in.seekg(0, std::ios::end);
  //Resize the wide string to be able to fit the entire file (Note: Do not use reserve()!).
  fileContents.resize(in.tellg());
  //Go back to the beginning of the file to start reading.
  in.seekg(0, std::ios::beg);
  //Read the entire file's contents into the wide string.
  in.read(fileContents.data(), fileContents.size());
  //Close the file.
  in.close();
  //Do whatever you want with the file contents.
  std::wcout << fileContents << L" " << fileContents.size();
  return true;
}

这将宽字符读入std::wstring，但如果您只想要常规字符和std::string，则可以很容易地进行调整。

Use

#include <iostream>
#include <sstream>
#include <fstream>

int main()
{
  std::ifstream input("file.txt");
  std::stringstream sstr;

  while(input >> sstr.rdbuf());

  std::cout << sstr.str() << std::endl;
}

或者非常接近。我自己没有打开stdlib引用来进行双重检查。

是的，我知道我没有按照要求写slurp函数。

该解决方案将错误检查添加到基于rdbuf()的方法中。

std::string file_to_string(const std::string& file_name)
{
    std::ifstream file_stream{file_name};

    if (file_stream.fail())
    {
        // Error opening file.
    }

    std::ostringstream str_stream{};
    file_stream >> str_stream.rdbuf();  // NOT str_stream << file_stream.rdbuf()

    if (file_stream.fail() && !file_stream.eof())
    {
        // Error reading file.
    }

    return str_stream.str();
}

I'm adding this answer because adding error-checking to the original method is not as trivial as you'd expect. The original method uses stringstream's insertion operator (str_stream << file_stream.rdbuf()). The problem is that this sets the stringstream's failbit when no characters are inserted. That can be due to an error or it can be due to the file being empty. If you check for failures by inspecting the failbit, you'll encounter a false positive when you read an empty file. How do you disambiguate legitimate failure to insert any characters and "failure" to insert any characters because the file is empty?

您可能会认为显式地检查空文件，但这是更多的代码和相关的错误检查。

检查失败条件str_stream.fail() && !str_stream.eof()不工作，因为插入操作没有设置eofbit(在ostringstream或ifstream上)。

所以，解决办法就是改变操作。不要使用ostringstream的插入操作符(<<)，而是使用ifstream的提取操作符(>>)，它确实设置了eofbit。然后检查失败条件file_stream.fail() && !file_stream.eof()。

重要的是，当file_stream >> str_stream.rdbuf()遇到合法的失败时，它不应该设置eofbit(根据我对规范的理解)。这意味着上述检查足以检测出合法的故障。

下面是一个使用新文件系统库的版本，它具有相当健壮的错误检查功能:

#include <cstdint>
#include <exception>
#include <filesystem>
#include <fstream>
#include <sstream>
#include <string>

namespace fs = std::filesystem;

std::string loadFile(const char *const name);
std::string loadFile(const std::string &name);

std::string loadFile(const char *const name) {
  fs::path filepath(fs::absolute(fs::path(name)));

  std::uintmax_t fsize;

  if (fs::exists(filepath)) {
    fsize = fs::file_size(filepath);
  } else {
    throw(std::invalid_argument("File not found: " + filepath.string()));
  }

  std::ifstream infile;
  infile.exceptions(std::ifstream::failbit | std::ifstream::badbit);
  try {
    infile.open(filepath.c_str(), std::ios::in | std::ifstream::binary);
  } catch (...) {
    std::throw_with_nested(std::runtime_error("Can't open input file " + filepath.string()));
  }

  std::string fileStr;

  try {
    fileStr.resize(fsize);
  } catch (...) {
    std::stringstream err;
    err << "Can't resize to " << fsize << " bytes";
    std::throw_with_nested(std::runtime_error(err.str()));
  }

  infile.read(fileStr.data(), fsize);
  infile.close();

  return fileStr;
}

std::string loadFile(const std::string &name) { return loadFile(name.c_str()); };

你可以使用我开发的第一个c++库来做到这一点:

#include "rst/files/file_utils.h"

std::filesystem::path path = ...;  // Path to a file.
rst::StatusOr<std::string> content = rst::ReadFile(path);
if (content.err()) {
  // Handle error.
}

std::cout << *content << ", " << content->size() << std::endl;

请看类似问题的答案。

为了方便大家，我转发了CTT的解决方案:

string readFile2(const string &fileName)
{
    ifstream ifs(fileName.c_str(), ios::in | ios::binary | ios::ate);

    ifstream::pos_type fileSize = ifs.tellg();
    ifs.seekg(0, ios::beg);

    vector<char> bytes(fileSize);
    ifs.read(bytes.data(), fileSize);

    return string(bytes.data(), fileSize);
}

当对《白鲸记》(Moby Dick, 1.3M)的文本进行平均100次运行时，该解决方案比本文给出的其他答案的执行时间快了约20%。对于一个可移植的c++解决方案来说还不错，我想看看mmap'ing文件的结果;)