C ++用条件语句读取文本文件 [英] C++ reading a text file with conditional statements
问题描述
我试图读取文本文件中的行,标记行,然后继续执行下一行的开关和中断块,但是在我的程序到达第一个中断之后,它退出循环,忽略文件的其余部分。
ifstream in(test.txt);
字符串行,缓冲区;
unsigned int firstLetter = 0;
// istringstream iss;
if(in.is_open())
{
istringstream iss;
while(getline(in,line))
{
iss.str(line);
char firstChar = line.at(firstLetter);
switch(firstChar)
{
case'D':
while(getline(iss,buffer,' - '))
{//打印每个令牌,每行一个
cout<<buffer:<< buffer<"<<< endl;
}
break;
case'R':
while(getline(iss,buffer,' - '))
{cout<<buffer:<<<<<<<<<<<<<<< ;< endl;}
break;
$ b 这是文本文件:
泰坦的D-Rise-25.50-2009-12
D-23 Jump Street-20.00 -2013-5
D-Home Alone-24.00-1995-16
D-Twin Warriors-24.00-2011-14
R-XXX-Pierce-Hawthorne-11-13
R-Forbidden Kingdom-Pierce-Hawthorne-13-31
R-23 Jump Street-Troy-Barnes-1-3
R-Home Alone-Shirley-Bennett-1-3
R-Modern Family-Abed-Nadir-10-66
但是当我运行我的代码时, :
$ $ p $ 缓冲区:D
缓冲区:Titans的上升
缓冲区:25.50
缓冲区:2009
buffer:12
这是文本文件中第1行的内容,我怎么能去到下一行,并继续这样做,直到文件的结尾?
你正在改变你的内容你的 std :: istringstream
对象,但是sta te标志保持为先前(即,你的eof位被点亮)。一个例子,使用你的输入数据通过stdin进行修改:
#include< iostream>
#include< fstream>
#include< sstream>
#include< string>
使用namespace std;
int main()
{
istream& in = std :: cin;
字符串行,缓冲区;
istringstream iss;
while(getline(in,line))
{
if(!line.empty())
{
iss.str(line);
std :: cout<< 在eof的行:<< iss.eof()<< \\\
;
char firstChar = line.at(0);
switch(firstChar)
{
case'D':
while(getline(iss,buffer,' - '))
cout <<<缓冲区: <<<<<<<<<<< endl;
break;
case'R':
while(getline(iss,buffer,' - '))
cout <<<缓冲区:<<<<<<<< << endl;
break;
$ b code
<输出
在eof的行:0
buffer:D
buffer:Rise Titans的
缓冲区:25.50
缓冲区:2009
缓冲区:12
eof的行:1
eof的行:1
eof的行: 1
线在eof:1
线在eof:1
线在eof:1
线在eof:1
线在eof:1
要解决这个问题,要么在每次迭代之前清除流的状态,要么只是在while循环内移动字符串流,用行初始化。前者在下面完成。我将后者作为一个练习:
#include< iostream>
#include< fstream>
#include< sstream>
#include< string>
使用namespace std;
int main()
{
istream& in = std :: cin;
字符串行,缓冲区;
istringstream iss; $())
while(getline(in,line))
{
if(!line.empty())
{
iss.clear(); //<< ===加到这里
iss.str(line);
std :: cout<< 在eof的行:<< iss.eof()<< \\\
;
char firstChar = line.at(0);
switch(firstChar)
{
case'D':
while(getline(iss,buffer,' - '))
cout <<<缓冲区: <<<<<<<<<<< endl;
break;
case'R':
while(getline(iss,buffer,' - '))
cout <<<缓冲区:<<<<<<<< << endl;
break;
$ b code
<输出
在eof的行:0
buffer:D
buffer:Rise Titans
buffer:25.50
buffer:2009
buffer:12
line at eof:0
buffer:D
buffer:23 Jump Street
缓冲区:20.00
缓冲区:2013
缓冲区:5
行eof:0
缓冲区:D
缓冲区:单独存放
缓冲区: 24.00
缓冲区:1995
缓冲区:16
行eof:0
缓冲区:D
缓冲区:双人战士
缓冲区:24.00
缓冲区:2011
缓冲区:14
行eof:0
缓冲区:R
缓冲区:XXX
缓冲区:Pierce
缓冲区:Hawthorne
缓冲区:11
缓冲区:13
行eof:0
缓冲区:R
缓冲区:禁止的王国
缓冲区:Pierce
缓冲区:Hawthorne
缓冲区:13
缓冲区:31
行eof:0
缓冲区:R
缓冲区:23跳转街
缓冲区:特洛伊
缓冲区:巴恩斯
缓冲区:1
缓冲区:3
行eof:0
缓冲区:R
缓冲区:单独存放
缓冲区:Shirley
缓冲区: Bennett
缓冲区:1
缓冲区:3
行eof:0
缓冲区:R
缓冲区:现代族
缓冲区:Abed
buffer:Nadir
buffer:10
buffer:66
I am trying to read lines in a text file, tokenize the line and then go on and do the same to the next line in a switch and break block, but after my program reaches the first break, it exits the loop and ignores the rest of the file.
ifstream in("test.txt");
string line,buffer;
unsigned int firstLetter = 0;
//istringstream iss;
if( in.is_open() )
{
istringstream iss;
while(getline(in,line))
{
iss.str(line);
char firstChar = line.at( firstLetter );
switch ( firstChar )
{
case 'D':
while (getline(iss,buffer,'-'))
{//print each token, one per line
cout<<"buffer: "<<buffer<<" "<<endl;
}
break;
case 'R':
while ( getline(iss,buffer,'-') )
{cout<<"buffer: "<<buffer<<" "<<endl;}
break;
}
}
}
this is the content of the text file:
D-Rise of the Titans-25.50-2009-12
D-23 Jump Street-20.00-2013-5
D-Home Alone-24.00-1995-16
D-Twin Warriors-24.00-2011-14
R-XXX-Pierce-Hawthorne-11-13
R-Forbidden Kingdom-Pierce-Hawthorne-13-31
R-23 Jump Street-Troy-Barnes-1-3
R-Home Alone-Shirley-Bennett-1-3
R-Modern Family-Abed-Nadir-10-66
but when i run my code i get this:
buffer: D
buffer: Rise of the Titans
buffer: 25.50
buffer: 2009
buffer: 12
which is the content of line 1 in the text file, how can i go to the next line and keep doing that till the end of the file?
解决方案 You're changing your content of your std::istringstream
object, but the state flags remain as prior (i.e., your eof bit is lit). An example, modified using your input data via stdin:
#include <iostream>
#include <fstream>
#include <sstream>
#include <string>
using namespace std;
int main()
{
istream& in = std::cin;
string line,buffer;
istringstream iss;
while(getline(in,line))
{
if (!line.empty())
{
iss.str(line);
std::cout << "line at eof: " << iss.eof() << '\n';
char firstChar = line.at(0);
switch ( firstChar )
{
case 'D':
while (getline(iss,buffer,'-'))
cout<<"buffer: "<<buffer<<" "<<endl;
break;
case 'R':
while ( getline(iss,buffer,'-') )
cout<<"buffer: "<<buffer<<" "<<endl;
break;
}
}
}
}
Output
line at eof: 0
buffer: D
buffer: Rise of the Titans
buffer: 25.50
buffer: 2009
buffer: 12
line at eof: 1
line at eof: 1
line at eof: 1
line at eof: 1
line at eof: 1
line at eof: 1
line at eof: 1
line at eof: 1
To fix this, either clear the state of the stream before each iteration, or just move the stringstream inside the while-loop, initialized with the line. The former is done below; I leave the latter as an exercise for you:
#include <iostream>
#include <fstream>
#include <sstream>
#include <string>
using namespace std;
int main()
{
istream& in = std::cin;
string line,buffer;
istringstream iss;
while(getline(in,line))
{
if (!line.empty())
{
iss.clear(); // <<=== ADDED HERE
iss.str(line);
std::cout << "line at eof: " << iss.eof() << '\n';
char firstChar = line.at(0);
switch ( firstChar )
{
case 'D':
while (getline(iss,buffer,'-'))
cout<<"buffer: "<<buffer<<" "<<endl;
break;
case 'R':
while ( getline(iss,buffer,'-') )
cout<<"buffer: "<<buffer<<" "<<endl;
break;
}
}
}
}
Output
line at eof: 0
buffer: D
buffer: Rise of the Titans
buffer: 25.50
buffer: 2009
buffer: 12
line at eof: 0
buffer: D
buffer: 23 Jump Street
buffer: 20.00
buffer: 2013
buffer: 5
line at eof: 0
buffer: D
buffer: Home Alone
buffer: 24.00
buffer: 1995
buffer: 16
line at eof: 0
buffer: D
buffer: Twin Warriors
buffer: 24.00
buffer: 2011
buffer: 14
line at eof: 0
buffer: R
buffer: XXX
buffer: Pierce
buffer: Hawthorne
buffer: 11
buffer: 13
line at eof: 0
buffer: R
buffer: Forbidden Kingdom
buffer: Pierce
buffer: Hawthorne
buffer: 13
buffer: 31
line at eof: 0
buffer: R
buffer: 23 Jump Street
buffer: Troy
buffer: Barnes
buffer: 1
buffer: 3
line at eof: 0
buffer: R
buffer: Home Alone
buffer: Shirley
buffer: Bennett
buffer: 1
buffer: 3
line at eof: 0
buffer: R
buffer: Modern Family
buffer: Abed
buffer: Nadir
buffer: 10
buffer: 66
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