从文件到字符串C ++读取任意长度的字节 [英] Read arbitrary-length bytes from file to string C++

问题描述

现在我对Python很熟悉，决定学习C ++，所以我非常n00b但肯定愿意学习。
我已经做了一个脚本从一个非常严格指定的文件格式（.EDF，医疗信号）读取，一个ascii头由字段大小定义。因此，我读取第一个字段的8个字节，第二个字段的80个字节，等等。

Now that I am quite familiar with Python, decided to learn C++, so I am very n00b but sure willing to learn. I had made a script to read from a very tightly-specified file format (.EDF, for medical signals), with an ascii header defined by field sizes in bytes. So, I read 8 bytes for the first field, 80 bytes for the second field, and so on.

我的工作python脚本如下：

My working python script is as follows:

## HEADER FIELD NAMES AND SIZES FROM EDF SPEC:
header_fields = (
('version',     8),    ('patinfo',    80),    ('recinfo',      80),
('start date',  8),    ('start time',  8),    ('header bytes',  8),
('reserved',   44),   ('nrecs',        8),    ('recduration',   8),
('nchannels', 4))

## TELL WHICH FILE TO OPEN
folder = os.path.expanduser('~/Dropbox/01MIOTEC/06APNÉIA/Samples')
f = open(folder + '/Osas2002plusQRS.rec', 'rb')

# READ FILE CONTENT TO DICTIONARY OF LABELLED FIELD CONTENTS,
# ALREADY STRIPPED FROM BLANK SPACES
header = {}
for key, value in header_fields:
    header[key] = f.read(value).strip()

最后的结果是'header'

The end result is 'header', a dictionary where each pair is a "labeled" string.

我目前的尴尬c ++代码，几乎可以工作打印到屏幕未刷新的字符串，这是：

My current awkward c++ code, which almost work printing to screen the unstripped strings, is this:

#include <iostream>
#include <fstream>
#include <string>

using namespace std;

static int header_bytes[] = {8,80,80,80,80,8,8,8,44,8,8,4};
static int header_bytes_len = sizeof(header_bytes)/sizeof(int);
static string header_fields[] =
{
    "version",     
    "patinfo",     
    "recinfo",     
    "patinfo",     
    "recifo",      
    "start date",  
    "start time",  
    "header bytes",
    "reserved",    
    "nrecs",       
    "rec duration",
    "nchannels"
};

int main()
{
    ifstream edfreader;
    edfreader.open("/home/helton/Dropbox/01MIOTEC/06APNÉIA/Samples/Osas2002plusQRS.rec", ios::binary);

    char * buffer = new char [80];
    for (int n = 0; n<header_bytes_len; n++)
    {
        edfreader.read(buffer, header_bytes[n]);
        buffer[header_bytes[n]] = '\0';
        cout<<"'"<<buffer<<"'"<<endl;
    }
    return 0;
}

实际上，我从cplusplus复制粘贴main（）的最后一部分.com论坛条目，只是为了获得某种输出，但实际上我想要的是将字段保存为字符串对象数组，或更好的数组指向字符串对象的指针。
我正在阅读C ++ Primer，但仍然在200多页，但我想严重地干扰一些c ++代码fiddling，所以如果任何人可以指向我一些方法或概念或读数，我会很高兴。

Actually, I copy-pasted the last part of main() from a cplusplus.com forum entry, just to get some kind of output, but actually what I wanted was to save the fields as an array of string objects, or better yet an array of pointers to string objects. I am reading "C++ Primer", but still in 200+ pages, but I want badly to fiddle with some c++ code fiddling, so if anyone could point me to some methods or concepts or readings, I would be very happy.

感谢阅读

推荐答案

假设没有空格除了填充字段，您可以使用以下方式将它们读入C ++字符串：

Assuming there are no spaces in the fields except for the padding, you can read them into C++ strings using:

/* Read field of n bytes */
std::string read_field(std::istream &edfreader, size_t n)
{
    // there's no need for new;
    // in fact, new may lead to a memory leak if you forget to delete
    std::vector<char> buf(n);

    // read as a sequence of bytes
    edfreader.read(&buf.front(), n);

    // find the first space or end of buffer
    size_t end = 0;
    while (end < n && buf[end] != ' ')
        end++;

    // make a string object from the buffer
    return std::string(buf, end);
}

std :: string 为你分配内存;你可以使用它很像一个Python字符串，除了它是可修改的。

std::string does memory allocation for you; you can use it pretty much like a Python string, except that it is modifiable.

这里唯一的假设是你的操作系统的字符集是一个超集且 edfreader 的异常处理已启用 code>。

The only assumptions made here are that your OS's character set is (a superset of) ASCII and that exception handling is on for edfreader.

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