C++ 计算文本文件中的行数
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counting the number of lines in a text file
提问by silent
I'm reading lines off of text file and I'm wondering if this is a good way to go? I had to write the function numberoflinesto decrease the number_of_lines variableby one because within the while loop, for every line it read it adds 2 to the number_of_lines variable.
我正在阅读文本文件中的行，我想知道这是否是一个好方法？我必须编写函数以将 thenumberoflines减number_of_lines variable一，因为在 while 循环中，对于它读取的每一行，它会将 2 添加到 number_of_lines 变量中。
#include <iostream>
#include <fstream>
using namespace std;
int number_of_lines = 0;
void numberoflines();
int main(){
string line;
ifstream myfile("textexample.txt");
if(myfile.is_open()){
while(!myfile.eof()){
getline(myfile,line);
cout<< line << endl;
number_of_lines++;
}
myfile.close();
}
numberoflines();
}
void numberoflines(){
number_of_lines--;
cout<<"number of lines in text file: " << number_of_lines << endl;
}
Is there any other easier better way?
还有其他更简单更好的方法吗？
回答by Jerry Coffin
Your hack of decrementing the count at the end is exactly that -- a hack.
你在最后减少计数的技巧就是——一个技巧。
Far better to write your loop correctly in the first place, so it doesn't count the last line twice.
首先正确编写循环要好得多，因此它不会将最后一行计算两次。
int main() {
int number_of_lines = 0;
std::string line;
std::ifstream myfile("textexample.txt");
while (std::getline(myfile, line))
++number_of_lines;
std::cout << "Number of lines in text file: " << number_of_lines;
return 0;
}
Personally, I think in this case, C-style code is perfectly acceptable:
就个人而言，我认为在这种情况下，C 风格的代码是完全可以接受的：
int main() {
unsigned int number_of_lines = 0;
FILE *infile = fopen("textexample.txt", "r");
int ch;
while (EOF != (ch=getc(infile)))
if ('\n' == ch)
++number_of_lines;
printf("%u\n", number_of_lines);
return 0;
}
Edit: Of course, C++ will also let you do something a bit similar:
编辑：当然，C++ 也会让你做一些类似的事情：
int main() {
std::ifstream myfile("textexample.txt");
// new lines will be skipped unless we stop it from happening:
myfile.unsetf(std::ios_base::skipws);
// count the newlines with an algorithm specialized for counting:
unsigned line_count = std::count(
std::istream_iterator<char>(myfile),
std::istream_iterator<char>(),
'\n');
std::cout << "Lines: " << line_count << "\n";
return 0;
}
回答by strager
I think your question is, "why am I getting one more line than there is in the file?"
我认为您的问题是，“为什么我得到的行比文件中的多一行？”
Imagine a file:
想象一个文件：
line 1
line 2
line 3
The file may be represented in ASCII like this:
该文件可以用 ASCII 表示，如下所示：
line 1\nline 2\nline 3\n
(Where \nis byte 0x10.)
（\n字节在哪里0x10。）
Now let's see what happens before and after each getlinecall:
现在让我们看看每次getline调用之前和之后会发生什么：
Before 1: line 1\nline 2\nline 3\n
Stream: ^
After 1: line 1\nline 2\nline 3\n
Stream: ^
Before 2: line 1\nline 2\nline 3\n
Stream: ^
After 2: line 1\nline 2\nline 3\n
Stream: ^
Before 2: line 1\nline 2\nline 3\n
Stream: ^
After 2: line 1\nline 2\nline 3\n
Stream: ^
Now, you'd think the stream would mark eofto indicate the end of the file, right? Nope! This is because getlinesets eofif the end-of-file marker is reached "during it's operation". Because getlineterminates when it reaches \n, the end-of-file marker isn't read, and eofisn't flagged. Thus, myfile.eof()returns false, and the loop goes through another iteration:
现在，您会认为流会标记eof以指示文件的结尾，对吗？不！这是因为getline设置eof是否在“操作期间”到达文件结束标记。因为getline在到达 时终止\n，文件结束标记不会被读取，eof也不会被标记。因此，myfile.eof()返回 false，循环进行另一次迭代：
Before 3: line 1\nline 2\nline 3\n
Stream: ^
After 3: line 1\nline 2\nline 3\n
Stream: ^ EOF
How do you fix this? Instead of checking for eof(), see if .peek()returns EOF:
你如何解决这个问题？与其检查eof()，不如查看是否.peek()返回EOF：
while(myfile.peek() != EOF){
getline ...
You can also check the return value of getline(implicitly casting to bool):
您还可以检查getline（隐式转换为 bool）的返回值：
while(getline(myfile,line)){
cout<< ...
回答by ashish
In C if you implement count line it will never fail. Yes you can get one extra line if there is stray "ENTER KEY"generally at the end of the file.
在 C 中，如果你实现计数线，它永远不会失败。是的，如果文件末尾通常有杂散的“ENTER KEY”，您可以获得额外的一行。
File might look some thing like this:
文件可能看起来像这样：
"hello 1
"Hello 2
"
Code below
下面的代码
#include <stdio.h>
#include <stdlib.h>
#define FILE_NAME "file1.txt"
int main() {
FILE *fd = NULL;
int cnt, ch;
fd = fopen(FILE_NAME,"r");
if (fd == NULL) {
perror(FILE_NAME);
exit(-1);
}
while(EOF != (ch = fgetc(fd))) {
/*
* int fgetc(FILE *) returns unsigned char cast to int
* Because it has to return EOF or error also.
*/
if (ch == '\n')
++cnt;
}
printf("cnt line in %s is %d\n", FILE_NAME, cnt);
fclose(fd);
return 0;
}
回答by Altinsystems
with for-loop:
使用 for 循环：
std::ifstream myFile;
std::string line;
int lines;
myFile.open(path);
for(lines = 0; std::getline(myFile,line); lines++);
std::cout << lines << std::endl;
