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()); };

这是我使用的函数，当处理大文件(1GB+)时，由于某种原因std::ifstream::read()比std::ifstream::rdbuf()快得多，当你知道文件大小时，所以整个“先检查文件大小”的事情实际上是一个速度优化

#include <string>
#include <fstream>
#include <sstream>
std::string file_get_contents(const std::string &$filename)
{
    std::ifstream file($filename, std::ifstream::binary);
    file.exceptions(std::ifstream::failbit | std::ifstream::badbit);
    file.seekg(0, std::istream::end);
    const std::streampos ssize = file.tellg();
    if (ssize < 0)
    {
        // can't get size for some reason, fallback to slower "just read everything"
        // because i dont trust that we could seek back/fourth in the original stream,
        // im creating a new stream.
        std::ifstream file($filename, std::ifstream::binary);
        file.exceptions(std::ifstream::failbit | std::ifstream::badbit);
        std::ostringstream ss;
        ss << file.rdbuf();
        return ss.str();
    }
    file.seekg(0, std::istream::beg);
    std::string result(size_t(ssize), 0);
    file.read(&result[0], std::streamsize(ssize));
    return result;
}

你可以使用'std::getline'函数，并指定'eof'作为分隔符。结果代码有点晦涩:

std::string data;
std::ifstream in( "test.txt" );
std::getline( in, data, std::string::traits_type::to_char_type( 
                  std::string::traits_type::eof() ) );

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;

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。

#include <string>
#include <sstream>

using namespace std;

string GetStreamAsString(const istream& in)
{
    stringstream out;
    out << in.rdbuf();
    return out.str();
}

string GetFileAsString(static string& filePath)
{
    ifstream stream;
    try
    {
        // Set to throw on failure
        stream.exceptions(fstream::failbit | fstream::badbit);
        stream.open(filePath);
    }
    catch (system_error& error)
    {
        cerr << "Failed to open '" << filePath << "'\n" << error.code().message() << endl;
        return "Open fail";
    }

    return GetStreamAsString(stream);
}

用法:

const string logAsString = GetFileAsString(logFilePath);