如何使用逗号分隔值对文本文件进行读写 [英] How to read-write into/from text file with comma separated values
问题描述
如果我的文件类似于逗号分隔值,则如何从文件中读取数据
1,2,3 ,4,5 \\\
6,7,8,9,10 \\\
\\\
并且在读取文件后,我想将数据写回其他文件,如同上面的格式。
,使用
字符串;
while(!file.eof()){
getline(file,line);
numlines ++;
}
numline--; //删除最后一个空行
但是如何知道行/行中的总位数?
我也有ints的向量来存储数据。
所以,我想读取第一行,然后计数该行中的元素总数,这里是5(1,2,3,4,5)并将它们存储在数组/向量中,并读取下一行和将它们重新存储在向量中等等,直到我到达EOF。
然后,我想把数据写入文件,我想这将做写作数据到文件,
numOfCols = 1;
for(int i = 0; i {
file< vector.at(i);
if((numOfCols< 5)file<<,; // print comma(,)
if((i + 1)%5 == 0)
{
file<< endl; //在第5个值后打印换行
numOfCols = 1; //从第1行开始,用于下一行
}
numOfCols ++;
}
文件<< endl; //上一个新行
我的主要问题是如何从文件读取数据用逗号分隔的值
感谢
步骤1:
不要这样做:
while(!file.eof ))
pre>
{
getline(file,line);
numlines ++;
}
numline--;
在尝试读取之前,EOF是不正确的。
标准模式是:while(getline(file,line))
{
++ numline;
}
还要注意,std :: getline()可以选择第三个参数,这是打破的字符。默认情况下这是行终止符,但您可以指定逗号。
while(getline(file,line))
{
std :: stringstream linestream(line);
std :: string value;
while(getline(linestream,value,','))
{
std :: cout< Value(<< value<<)\\\
;
}
std :: cout<< Line Finished<< std :: endl;
}
如果将所有值存储在一个向量中,它们使用固定宽度。然后我会这样做。
struct LineWriter
{
LineWriter(std :: ostream& str,int size)
:m_str(str)
,m_size(size)
,m_current(0)
{}
// std :: copy()赋值给迭代器。
//看起来像这样(* result)=< value> ;;
//因此覆盖运算符*和运算符= to
LineWriter&运算符*(){return * this;}
void operator =(int val)
{
++ m_current;
m_str<< val<< (((m_current%m_size)== 0)?\\\
:,);
}
// std :: copy()递增迭代器。但是这不是usfull这里
//所以只是实现太空的方法来处理增量。
void operator ++(){}
void operator ++(int){}
//本地数据。
std :: ostream& m_str;
int const m_size;
int m_current;
};
void printCommaSepFixedSizeLinesFromVector(std :: vector const& data,int linesize)
{
std :: copy(data.begin(),data.end(),LineWriter std :: cout,linesize));
}
How do I read data from a file if my file is like this with comma separated values
1, 2, 3, 4, 5\n 6, 7, 8, 9, 10\n \n
and after reading the file, I want to write the data back into other file as same format above.
I can get total number of lines, using
string line; while(!file.eof()){ getline(file,line); numlines++; } numline--; // remove the last empty line
but how can I know total number of digits in a row/line ??
I also have vector of ints to store the data. So, I want to read the first line and then count total number of elements in that line, here 5 (1,2,3,4,5) and store them in array/vector, and read next line and store them in vector again and so on till I reach EOF.
Then, I want to write the data to file, again, I guess this will do the job of writing data to file,
numOfCols=1; for(int i = 0; i < vector.size(); i++) { file << vector.at(i); if((numOfCols<5) file << ",";//print comma (,) if((i+1)%5==0) { file << endl;//print newline after 5th value numOfCols=1;//start from column 1 again, for the next line } numOfCols++; } file << endl;// last new line
So, my main problem is how to read the data from file with comma separated values ??
Thanks
解决方案Step 1: Dont do this:
while(!file.eof()) { getline(file,line); numlines++; } numline--;
The EOF is not true until you try and read past it.
The standard pattern is:while(getline(file,line)) { ++numline; }
Also note that std::getline() can optinally take a third parameter. This is the character to break on. By default this is the line terminator but you can specify a comma.
while(getline(file,line)) { std::stringstream linestream(line); std::string value; while(getline(linestream,value,',')) { std::cout << "Value(" << value << ")\n"; } std::cout << "Line Finished" << std::endl; }
If you store all the values in a single vector then print them out using a fixed width. Then I would do somthing like this.
struct LineWriter { LineWriter(std::ostream& str,int size) :m_str(str) ,m_size(size) ,m_current(0) {} // The std::copy() does assignement to an iterator. // This looks like this (*result) = <value>; // So overide the operator * and the operator = to LineWriter& operator*() {return *this;} void operator=(int val) { ++m_current; m_str << val << (((m_current % m_size) == 0)?"\n":","); } // std::copy() increments the iterator. But this is not usfull here // so just implement too empty methods to handle the increment. void operator++() {} void operator++(int) {} // Local data. std::ostream& m_str; int const m_size; int m_current; }; void printCommaSepFixedSizeLinesFromVector(std::vector const& data,int linesize) { std::copy(data.begin(),data.end(),LineWriter(std::cout,linesize)); }
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