C++ 将文件加载到 vector<char>
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原文地址: http://stackoverflow.com/questions/7241871/
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Loading a file into a vector<char>
提问by Mankarse
I would like to load the contents of a text file into a vector<char>(or into any char input iterator, if that is possible). Currently my code looks like this:
我想将文本文件的内容加载到 a vector<char>（或任何字符输入迭代器，如果可能的话）。目前我的代码如下所示：
std::vector<char> vec;
std::ifstream file("test.txt");
assert(file.is_open());
while (!(file.eof() || file.fail())) {
char buffer[100];
file.read(buffer, 100);
vec.insert(vec.end(), buffer, buffer + file.gcount());
}
I do not like the manual use of a buffer (Why 100 chars? Why not 200, or 25 or whatever?), or the large number of lines that this took. The code just seems very ugly and non-C++. Is there a more direct way of doing this?
我不喜欢手动使用缓冲区（为什么是 100 个字符？为什么不是 200，或 25 或其他？），或者这需要大量的行。代码看起来非常丑陋且非 C++。有没有更直接的方法来做到这一点？
采纳答案by Flexo
Another approach, using rdbuf()to read the whole file to a std::stringstreamfirst:
另一种方法，用于rdbuf()首先读取整个文件std::stringstream：
#include <fstream>
#include <sstream>
#include <vector>
#include <string>
// for check:
#include <algorithm>
#include <iterator>
#include <iostream>
int main() {
std::ifstream file("test.cc");
std::ostringstream ss;
ss << file.rdbuf();
const std::string& s = ss.str();
std::vector<char> vec(s.begin(), s.end());
// check:
std::copy(vec.begin(), vec.end(), std::ostream_iterator<char>(std::cout));
}
回答by hamstergene
If you want to avoid reading char by char:
如果您想避免逐个字符读取字符：
if (!file.eof() && !file.fail())
{
file.seekg(0, std::ios_base::end);
std::streampos fileSize = file.tellg();
vec.resize(fileSize);
file.seekg(0, std::ios_base::beg);
file.read(&vec[0], fileSize);
}
回答by KillianDS
I think it's something like this, but have no environment to test it:
我认为它是这样的，但没有环境可以测试它：
std::copy(std::istream_iterator<char>(file), std::istream_iterator<char>(), std::back_inserter(vec));
Could be you have to play with io manipulators for things like linebreaks/whitespace.
可能你必须使用 io 操纵器来处理换行符/空格之类的事情。
Edit: as noted in comments, could be a performance hit.
编辑：如评论中所述，可能会影响性能。
回答by Adrien Plisson
use an iterator:
使用迭代器：
#include <iterator>
istream_iterator<char> data( file );
istream_iterator<char> end;
vec.insert( std::back_inserter(vec), data, end );
回答by Mankarse
There were lots of good responses. Thanks all! The code that I have decided on using is this:
有很多很好的回应。谢谢大家！我决定使用的代码是这样的：
std::vector<char> vec;
std::ifstream file;
file.exceptions(
std::ifstream::badbit
| std::ifstream::failbit
| std::ifstream::eofbit);
//Need to use binary mode; otherwise CRLF line endings count as 2 for
//`length` calculation but only 1 for `file.read` (on some platforms),
//and we get undefined behaviour when trying to read `length` characters.
file.open("test.txt", std::ifstream::in | std::ifstream::binary);
file.seekg(0, std::ios::end);
std::streampos length(file.tellg());
if (length) {
file.seekg(0, std::ios::beg);
vec.resize(static_cast<std::size_t>(length));
file.read(&vec.front(), static_cast<std::size_t>(length));
}
Obviously, this is not suitable for extremely large files or performance-critical code, but it is good enough for general purpose use.
显然，这不适合超大文件或性能关键代码，但对于通用用途来说已经足够了。
