So the teacher has posed this assignment:
所以老师提出了这个任务:
You have been hired by the United Network Command for Law Enforcement, and you have been given files containing null cyphers you have to decrypt.
您已被联合网络执法司令部聘用,并且您已获得包含您必须解密的空密码的文件。
So for the first file given (as an example), every other letter is correct (ie: 'hielqlpo' is hello (assuming you start with the first letter). My first question is, how do I read in a file? The document is on my desktop in a folder and the file is named document01.cry. I'm not sure the command I need to put that file into the program.
因此,对于给出的第一个文件(作为示例),每隔一个字母都是正确的(即:'hielqlpo'是hello(假设您从第一个字母开始)。我的第一个问题是,如何读取文件?文档在我的桌面上的文件夹中,文件名为document01.cry。我不确定我需要将该文件放入程序的命令。
I'm also not overly sure how to grab a letter and skip a letter, but honestly I want to tinker with that before I post that question! So for now...my question is as stated in the title: How do you grab a file for reading in C++?
我也不太确定如何抓住一封信并跳过一封信,但说实话,我想在发布这个问题之前修补一下!所以现在...我的问题如标题所述:你如何获取一个用C ++阅读的文件?
If it makes a difference (As I'm sure it does), I'm using Visual C++ 2008 Express Edition (because it's free and I like it! I've also attached what I have so far, please keep in mind it's -very- basic...and I added the getchar(); at the end so when it does run properly, the window stays open so I can see it (as Visual Express tends to close the window as soon as it's done running.)
如果它有所作为(我确定它确实如此),我正在使用Visual C ++ 2008 Express Edition(因为它是免费的,我喜欢它!我还附上了我迄今为止的内容,请记住它是 - 非常基本......我在最后添加了getchar();所以当它运行正常时,窗口保持打开状态,所以我可以看到它(因为Visual Express在运行完毕后会逐渐关闭窗口。)
The code so far:
到目前为止的代码:
#include<iostream>
using namespace std;
int main()
{
while (! cin.eof())
{
int c = cin.get() ;
cout.put(c) ;
}
getchar();
}
PS: I realize that this code grabs and puts out every character. For now that's fine, once I can read in the file I think I can tinker with it from there. I'm also poking at a book or two I have on C++ to see it anything pops up and screams "Pick me!" Thanks again!
PS:我意识到这段代码可以抓住每一个角色。现在这很好,一旦我可以阅读文件,我想我可以从那里修补它。我也在用C ++上的一两本书来看看它弹出的任何东西并尖叫着“接我!”再次感谢!
EDIT:: Also curious, is there a way to input the file you want? (I.e.:
编辑::也很好奇,有没有办法输入你想要的文件? (即:
char filename;
cout << "Please make sure the document is in the same file as the program, thank you!" << endl << "Please input document name: " ;
cin >> filename;
cout << endl;
ifstream infile(filename, ios::in);
This code doesn't work. It shoots back an error saying the char can't be converted to a const char *. How can this problem be fixed?
此代码不起作用。它发回一个错误,说char不能转换为const char *。如何解决这个问题?
EDIT 2: Never mind about said part 2, I found it out! Thanks again for the assistance!
编辑2:没关系说第2部分,我发现了!再次感谢您的帮助!
5 个解决方案
#1
To do file operations, you need the correct include:
要进行文件操作,您需要正确的包含:
#include <fstream>
Then, in your main function, you can open a file stream:
然后,在您的main函数中,您可以打开文件流:
ifstream inFile( "filename.txt", ios::in );
or, for output:
或者,对于输出:
ofstream outFile( "filename.txt", ios::out );
You can then use inFile as you would use cin, and outFile as you would use cout. To close the file when you are done:
然后你就像使用cin一样使用inFile,而使用cout则使用outFile。完成后关闭文件:
inFile.close();
outFile.close();
#3
[EDIT] include support for command line arguments [EDIT] Fixed possible memory leak [EDIT] Fixed a missing reference
[编辑]包括对命令行参数的支持[编辑]修复了可能的内存泄漏[编辑]修复了缺少的参考
#include <fstream>
#include <iostream>
using namespace std;
int main(int argc, char *argv){
ifstream infh; // our file stream
char *buffer;
for(int c = 1; c < argc; c++){
infh.open(argv[c]);
//Error out if the file is not open
if(!infh){
cerr << "Could not open file: "<< argv[c] << endl;
continue;
}
//Get the length of the file
infh.seekg(0, ios::end);
int length = infh.tellg();
//reset the file pointer to the beginning
is.seekg(0, ios::beg);
//Create our buffer
buffer = new char[length];
// Read the entire file into the buffer
infd.read(buffer, length);
//Cycle through the buffer, outputting every other char
for(int i=0; i < length; i+= 2){
cout << buffer[i];
}
infh.close();
}
//Clean up
delete[] buffer;
return 0;
}
Should do the trick. If the file is extremely large, you probably shouldn't load the entire file into the buffer.
应该做的伎俩。如果文件非常大,您可能不应该将整个文件加载到缓冲区中。
#4
Although your queston has been answered, two little tips: 1) Instead of counting x and y to see if you are on an odd or even character you can do the following:
虽然你的问题得到了回答,但有两点小提示:1)你可以做以下事情,而不是计算x和y以查看你是否处于奇数或偶数字符。
int count=0;
while(!infile.eof())
{
infile.get(letter);
count++;
if(count%2==0)
{
cout<<letter;
}
}
% essentially means 'remainder when divided by,' so 11%3 is two. in the above it gives odd or even.
%本质上是指“除以时的余数”,因此11%3为2。在上面它给出奇数或偶数。
2) Assuming you only need to run it on windows:
2)假设你只需要在windows上运行它:
system("pause");
will make the window stay open when its finished running so you don't need the last getchar() call (you may have to #include<Windows.h> for that to work).
将使窗口在完成运行时保持打开状态,因此您不需要最后一次getchar()调用(您可能需要#include
#5
I figured it out! To be honest no one answer helped, it was a combination of the three, plus the comments from them. Thank you all very much! I've attached the code I used, as well as a copy of the document. The program reads in every character, then spits out the deciphered text. (IE: 1h.e0l/lqo is hello) The next step (extra credit) is to set it up so the user inputs how many characters to skip before reading in the next character to input.
我想到了!说实话,没有人回答过,这是三者的结合,加上他们的评论。非常感谢你们!我附上了我使用的代码,以及文档的副本。程序读入每个字符,然后吐出解密的文本。 (IE:1h.e0l / lqo是你好)下一步(额外功劳)是设置它,以便用户输入要在输入下一个字符之前跳过的字符数。
This step I intend to do on my own, but again, thank you very much for all the assistance everyone! Proving once again how awesome this site is, one line of code at a time!
这一步我打算独自完成,但再次感谢大家的帮助!再次证明这个网站有多棒,一次一行代码!
EDIT:: Code adjusted to accept user input, as well as allow for multiple uses without recompiling (I realize it looks like a huge sloppy mess, but that's why it's EXTREMELY commented...because in my mind it looks nice and neat)
编辑::代码调整为接受用户输入,以及允许多次使用而无需重新编译(我意识到它看起来像一个巨大的草率混乱,但这就是为什么它非常评论...因为在我看来它看起来很漂亮和整洁)
#include<iostream>
#include<fstream> //used for reading/writing to files, ifstream could have been used, but used fstream for that 'just in case' feeling.
#include<string> //needed for the filename.
#include<stdio.h> //for goto statement
using namespace std;
int main()
{
program:
char choice; //lets user choose whether to do another document or not.
char letter; //used to track each character in the document.
int x = 1; //first counter for tracking correct letter.
int y = 1; //second counter (1 is used instead of 0 for ease of reading, 1 being the "first character").
int z; //third counter (used as a check to see if the first two counters are equal).
string filename; //allows for user to input the filename they wish to use.
cout << "Please make sure the document is in the same file as the program, thank you!" << endl << "Please input document name: " ;
cin >> filename; //getline(cin, filename);
cout << endl;
cout << "'Every nth character is good', what number is n?: ";
cin >> z; //user inputs the number at which the character is good. IE: every 5th character is good, they would input 5.
cout << endl;
z = z - 1; //by subtracting 1, you now have the number of characters you will be skipping, the one after those is the letter you want.
ifstream infile(filename.c_str()); //gets the filename provided, see below for incorrect input.
if(infile.is_open()) //checks to see if the file is opened.
{
while(!infile.eof()) //continues looping until the end of the file.
{
infile.get(letter); //gets the letters in the order that that they are in the file.
if (x == y) //checks to see if the counters match...
{
x++; //...if they do, adds 1 to the x counter.
}
else
{
if((x - y) == z) //for every nth character that is good, x - y = nth - 1.
{
cout << letter; //...if they don't, that means that character is one you want, so it prints that character.
y = x; //sets both counters equal to restart the process of counting.
}
else //only used when more than every other letter is garbage, continues adding 1 to the first
{ //counter until the first and second counters are equal.
x++;
}
}
}
cout << endl << "Decryption complete...if unreadable, please check to see if your input key was correct then try again." << endl;
infile.close();
cout << "Do you wish to try again? Please press y then enter if yes (case senstive).";
cin >> choice;
if(choice == 'y')
{
goto program;
}
}
else //this prints out and program is skipped in case an incorrect file name is used.
{
cout << "Unable to open file, please make sure the filename is correct and that you typed in the extension" << endl;
cout << "IE:" << " filename.txt" << endl;
cout << "You input: " << filename << endl;
cout << "Do you wish to try again? Please press y then enter if yes (case senstive)." ;
cin >> choice;
if(choice == 'y')
{
goto program;
}
}
getchar(); //because I use visual C++ express.
}
EDIT:::
I tried inserting the text, but I couldn't get it to come out right, it kept treating some of the characters like coding (ie an apostrophe apparently is the equivalent of the bold command), but you could just try putting in "0h1e.l9lao" without the parenthesis into a .txt and it should give the same outcome.
我尝试插入文本,但我无法让它出来正确,它一直在处理一些字符,如编码(即撇号显然相当于粗体命令),但你可以尝试输入“0h1e .l9lao“没有括号到.txt,它应该给出相同的结果。
Thanks again everyone for the help!
再次感谢大家的帮助!
#1
To do file operations, you need the correct include:
要进行文件操作,您需要正确的包含:
#include <fstream>
Then, in your main function, you can open a file stream:
然后,在您的main函数中,您可以打开文件流:
ifstream inFile( "filename.txt", ios::in );
or, for output:
或者,对于输出:
ofstream outFile( "filename.txt", ios::out );
You can then use inFile as you would use cin, and outFile as you would use cout. To close the file when you are done:
然后你就像使用cin一样使用inFile,而使用cout则使用outFile。完成后关闭文件:
inFile.close();
outFile.close();
#2
C ++:带文件的输入/输出
#3
[EDIT] include support for command line arguments [EDIT] Fixed possible memory leak [EDIT] Fixed a missing reference
[编辑]包括对命令行参数的支持[编辑]修复了可能的内存泄漏[编辑]修复了缺少的参考
#include <fstream>
#include <iostream>
using namespace std;
int main(int argc, char *argv){
ifstream infh; // our file stream
char *buffer;
for(int c = 1; c < argc; c++){
infh.open(argv[c]);
//Error out if the file is not open
if(!infh){
cerr << "Could not open file: "<< argv[c] << endl;
continue;
}
//Get the length of the file
infh.seekg(0, ios::end);
int length = infh.tellg();
//reset the file pointer to the beginning
is.seekg(0, ios::beg);
//Create our buffer
buffer = new char[length];
// Read the entire file into the buffer
infd.read(buffer, length);
//Cycle through the buffer, outputting every other char
for(int i=0; i < length; i+= 2){
cout << buffer[i];
}
infh.close();
}
//Clean up
delete[] buffer;
return 0;
}
Should do the trick. If the file is extremely large, you probably shouldn't load the entire file into the buffer.
应该做的伎俩。如果文件非常大,您可能不应该将整个文件加载到缓冲区中。
#4
Although your queston has been answered, two little tips: 1) Instead of counting x and y to see if you are on an odd or even character you can do the following:
虽然你的问题得到了回答,但有两点小提示:1)你可以做以下事情,而不是计算x和y以查看你是否处于奇数或偶数字符。
int count=0;
while(!infile.eof())
{
infile.get(letter);
count++;
if(count%2==0)
{
cout<<letter;
}
}
% essentially means 'remainder when divided by,' so 11%3 is two. in the above it gives odd or even.
%本质上是指“除以时的余数”,因此11%3为2。在上面它给出奇数或偶数。
2) Assuming you only need to run it on windows:
2)假设你只需要在windows上运行它:
system("pause");
will make the window stay open when its finished running so you don't need the last getchar() call (you may have to #include<Windows.h> for that to work).
将使窗口在完成运行时保持打开状态,因此您不需要最后一次getchar()调用(您可能需要#include
#5
I figured it out! To be honest no one answer helped, it was a combination of the three, plus the comments from them. Thank you all very much! I've attached the code I used, as well as a copy of the document. The program reads in every character, then spits out the deciphered text. (IE: 1h.e0l/lqo is hello) The next step (extra credit) is to set it up so the user inputs how many characters to skip before reading in the next character to input.
我想到了!说实话,没有人回答过,这是三者的结合,加上他们的评论。非常感谢你们!我附上了我使用的代码,以及文档的副本。程序读入每个字符,然后吐出解密的文本。 (IE:1h.e0l / lqo是你好)下一步(额外功劳)是设置它,以便用户输入要在输入下一个字符之前跳过的字符数。
This step I intend to do on my own, but again, thank you very much for all the assistance everyone! Proving once again how awesome this site is, one line of code at a time!
这一步我打算独自完成,但再次感谢大家的帮助!再次证明这个网站有多棒,一次一行代码!
EDIT:: Code adjusted to accept user input, as well as allow for multiple uses without recompiling (I realize it looks like a huge sloppy mess, but that's why it's EXTREMELY commented...because in my mind it looks nice and neat)
编辑::代码调整为接受用户输入,以及允许多次使用而无需重新编译(我意识到它看起来像一个巨大的草率混乱,但这就是为什么它非常评论...因为在我看来它看起来很漂亮和整洁)
#include<iostream>
#include<fstream> //used for reading/writing to files, ifstream could have been used, but used fstream for that 'just in case' feeling.
#include<string> //needed for the filename.
#include<stdio.h> //for goto statement
using namespace std;
int main()
{
program:
char choice; //lets user choose whether to do another document or not.
char letter; //used to track each character in the document.
int x = 1; //first counter for tracking correct letter.
int y = 1; //second counter (1 is used instead of 0 for ease of reading, 1 being the "first character").
int z; //third counter (used as a check to see if the first two counters are equal).
string filename; //allows for user to input the filename they wish to use.
cout << "Please make sure the document is in the same file as the program, thank you!" << endl << "Please input document name: " ;
cin >> filename; //getline(cin, filename);
cout << endl;
cout << "'Every nth character is good', what number is n?: ";
cin >> z; //user inputs the number at which the character is good. IE: every 5th character is good, they would input 5.
cout << endl;
z = z - 1; //by subtracting 1, you now have the number of characters you will be skipping, the one after those is the letter you want.
ifstream infile(filename.c_str()); //gets the filename provided, see below for incorrect input.
if(infile.is_open()) //checks to see if the file is opened.
{
while(!infile.eof()) //continues looping until the end of the file.
{
infile.get(letter); //gets the letters in the order that that they are in the file.
if (x == y) //checks to see if the counters match...
{
x++; //...if they do, adds 1 to the x counter.
}
else
{
if((x - y) == z) //for every nth character that is good, x - y = nth - 1.
{
cout << letter; //...if they don't, that means that character is one you want, so it prints that character.
y = x; //sets both counters equal to restart the process of counting.
}
else //only used when more than every other letter is garbage, continues adding 1 to the first
{ //counter until the first and second counters are equal.
x++;
}
}
}
cout << endl << "Decryption complete...if unreadable, please check to see if your input key was correct then try again." << endl;
infile.close();
cout << "Do you wish to try again? Please press y then enter if yes (case senstive).";
cin >> choice;
if(choice == 'y')
{
goto program;
}
}
else //this prints out and program is skipped in case an incorrect file name is used.
{
cout << "Unable to open file, please make sure the filename is correct and that you typed in the extension" << endl;
cout << "IE:" << " filename.txt" << endl;
cout << "You input: " << filename << endl;
cout << "Do you wish to try again? Please press y then enter if yes (case senstive)." ;
cin >> choice;
if(choice == 'y')
{
goto program;
}
}
getchar(); //because I use visual C++ express.
}
EDIT:::
I tried inserting the text, but I couldn't get it to come out right, it kept treating some of the characters like coding (ie an apostrophe apparently is the equivalent of the bold command), but you could just try putting in "0h1e.l9lao" without the parenthesis into a .txt and it should give the same outcome.
我尝试插入文本,但我无法让它出来正确,它一直在处理一些字符,如编码(即撇号显然相当于粗体命令),但你可以尝试输入“0h1e .l9lao“没有括号到.txt,它应该给出相同的结果。
Thanks again everyone for the help!
再次感谢大家的帮助!