我如何读一个文件到一个std::字符串，即，读取整个文件一次?
文本或二进制模式应该由调用者指定。解决方案应该是符合标准的、可移植的和高效的。它不应该不必要地复制字符串的数据，并且应该避免在读取字符串时重新分配内存。
一种方法是统计文件大小，调整std::string和fread()到std::string的const_cast<char*>()'ed data()。这要求std::string的数据是连续的，这不是标准所要求的，但它似乎是所有已知实现的情况。更糟糕的是，如果以文本模式读取文件，std::string的大小可能不等于文件的大小。
一个完全正确的、符合标准的、可移植的解决方案可以使用std::ifstream的rdbuf()构造成std::ostringstream，再从那里构造成std::string。但是，这可能会复制字符串数据和/或不必要地重新分配内存。
是否所有相关的标准库实现都足够智能以避免所有不必要的开销?
还有别的办法吗?
我是否错过了一些已经提供所需功能的隐藏Boost函数?
void slurp(std::string& data, bool is_binary)
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。
就性能而言，我还没有找到比下面的代码更快的代码。
std::string readAllText(std::string const &path)
{
assert(path.c_str() != NULL);
FILE *stream = fopen(path.c_str(), "r");
assert(stream != NULL);
fseek(stream, 0, SEEK_END);
long stream_size = ftell(stream);
fseek(stream, 0, SEEK_SET);
void *buffer = malloc(stream_size);
fread(buffer, stream_size, 1, stream);
assert(ferror(stream) == 0);
fclose(stream);
std::string text((const char *)buffer, stream_size);
assert(buffer != NULL);
free((void *)buffer);
return text;
}
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。
