I can get the characters from console with this code:
Displays 2 characters each time in a new line
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
int main()
{
char ch[3] = "";
ifstream file("example.txt");
while (file.read(ch, sizeof(ch)-1))
{
cout << ch << endl;
}
return 0;
}
My problem is, if the set of characters be odd it doesn't displays the last character in the text file!
my text file contains this:
abcdefg
it doesn't displays the letter g in the console
its displaying this:
ab
cd
ef
I wanna display like this:
ab
cd
ef
g
I wanna use this to read 1000 characters at a time for a large file so i don't wanna read character by character, It takes a lot of time, but it has a problem if u can fix it or have a better suggestion, share it with me
The following piece of code should work:
while (file) {
file.read(ch, sizeof(ch) - 1);
int number_read_chars = file.gcount();
// print chars here ...
}
By moving the read call into the loop, you'll be able to handle the last call, where too few characters are available. The gcount method will provide you with the information how many characters were actually read by the last unformatted input operation, e.g. read.
Please note, when reading less than sizeof(ch) chars, you manually have to insert a NUL character at the position returned by gcount, if you intend to use the buffer as a C string, as those are null terminated:
ch[file.gcount()] = '\0';
Related
In my code bellow CODE 1 reading HEX from a file and storing in in string array won't convert it to ASCII when printed out.
#include <iostream>
#include <sstream>
#include <fstream>
int main(int argc, char** argv)
{
// CODE 1
std::ifstream input("C:\\test.txt"); // The test.txt contains \x48\x83\xEC\x28\x48\x83
std::stringstream sstr;
input >> sstr.rdbuf();
std::string test = sstr.str();
std::cout << "\nString from file: " << test;
//char* lol = new char[test.size()];
//memcpy(lol, test.data(), test.size());
////////////////////////////////////////////////////////
// CODE 2
std::string test_2 = "\x48\x83\xEC\x28\x48\x83";
std::cout << "\n\nHardcoded string: " << test_2 << "\n";
// Prints as ASCII "H(H" , which I want my CODE 1 to do.
}
In my CODE 2 sample, same HEX is used and it prints it as ASCII. Why is it not the same for CODE 1?
Okay, it looks like there is some confusion. First, I have to ask if you're SURE you know what is in your file.
That is, does it contain, oh, it looks like about 20 characters:
\
x
4
8
et cetera?
Or does it contain a hex 48 (one byte), a hex 83 (one byte), for a total of 5-ish characters?
I bet it's the first. I bet your file is about 20 characters long and literally contains the string that's getting printed.
And if so, then the code is doing what you expect. It's reading a line of text and writing it back out. If you want it to actually interpret it like the compiler does, then you're going to have to do the steps yourself.
Now, if it actually contains the hex characters (but I bet it doesn't), then that's a little different problem, and we'll have to look at that. But I think you just have a string of characters that includes \x in it. And reading / writing that isn't going to automatically do some magic for you.
When you read from file, the backslash characters are not escaped. Your test string from file is literally an array of chars: {'\\', 'x', '4', '8', ... }
Whereas your hardcoded literal string, "\x48\x83\xEC\x28\x48\x83"; is fully hex escaped by the compiler.
If you really want to store your data as a text file as a series of "backslash x NN" sequences, you'll need to convert after you read from file. Here's a hacked up loop that would do it for you.
std::string test = sstr.str();
char temp[3] = {};
size_t t = 0;
std::string corrected;
for (char c : test)
{
if (isxdigit(c))
{
temp[t] = c;
t++;
if (t == 2)
{
t = 0;
unsigned char uc = (unsigned char)strtoul(tmp, nullptr, 16);
corrected += (char)uc;
}
}
}
You can split the returned string in \x then make casting from string to int,
finally casting to char.
this resource will be helpful
strtok And convert
#include <iostream>
#include <fstream>
#include <sstream>
#include <string>
#include <iomanip>
void add1(std::fstream& files)
{
char c;
int i=0;
int j=0;
int k=0;
int con=0;
string word;
while(files.get(c)&&!files.eof())
{
i++;
j++;
if(c=='\n'||(con>=1&&isspace(c)))
{
con++;
if(con>=2)
{
break;
}
else
{
cout<<j<<"\/"<<i<<endl;
files.seekp(i-j,files.beg);
files.write("h",1);
files.seekg(i);
*seekg ends the loops I tried fstream::clear. I think it would work perfect if seekg worked.
+ without seekg it works but only for 3 lines then its off.
j=0;
word="";
}
}
else
{
con=0;
word=word+c;
}
}
}
*The goal is to be able stream the file, and replace the first letter of every line in the file while streaming.*
You seam to have a logical error and make thinks overcomplicated.
I do not knwow, what you want to do with your variable "word". It is consumed nowhere. So, I will ignore it.
Then you are playing with read and write pointers. That is not necessary. You only need to manipulate the write pointer.
Then, you want to "stream" something. This I do not fully understand. Maybe it means, that you want to write always something to the stream, even, if you do not replace anything. This would in my understanding only make sense, if you would have 2 streams. But in that case it would be brutally simple and no further thinking necessary.
If we use the same stream and do not want to replace a character, then this is already there, existing, and maybe not overwritten by the same character again.
So, if there is nothing to replace, then we will write nothing . . .
Also, and that is very important, we do no replacement operation, if we have an empty line, because then there is nothing to replace. There is now first character in an empty line.
And, most important, we cannot add characters to the same fstream. In that case we would have to shift the rest of the file one to the right. Therefore. 2 streams are always better. Then, this problem would not occur.
So, what's the logic.
Algorithm:
We always look at the previuosly read character. If that was a '\n' and the current character is not, then we are now in a new line and can replace the first character.
That is all.
It will take also into account, if a '\n' is encoded with 2 characters (for example \r\n). It will always work.
And, it is easy to implement. 10 lines of code.
Please see:
#include <iostream>
#include <fstream>
#include <string>
constexpr char ReplacementCharacter{ 'h' };
void replaceFirstCharacterOfLine(std::fstream& fileStream) {
// Here we stor the previously read character. In the beginning, a file always starts
// with a newline. Therefore we pretend that the last read character is a newline
char previouslyReadCharacter{'\n'};
// Here we store the current read character
char currentCharacter{};
// Get characters from file as lon as there are characters, so, until eof
while (fileStream.get(currentCharacter)) {
// No check, if a new line has started. We ignore empty lines!
if ((previouslyReadCharacter == '\n') && (currentCharacter != '\n')) {
// So last charcter was a newline and this is different. So, we are in a new, none empty line
// Set replacement character
currentCharacter = ReplacementCharacter;
// Go one back with the write pointer
fileStream.seekp(-1, std::ios_base::cur);
// Write (an with taht increment file pointer again)
fileStream.put(currentCharacter);
// Write to file
fileStream.flush();
}
else {
// Do not replace the first charcater. So nothing to be done here
}
// Now, set the previouslyReadCharacter to the just read currentCharacter
previouslyReadCharacter = currentCharacter;
}
}
int main() {
const std::string filename{"r:\\replace.txt"};
// Open file
std::fstream fileStream{ filename };
// Check, if file could be opened
if (fileStream)
replaceFirstCharacterOfLine(fileStream);
else
std::cerr << "\n\n*** Error: Could not open file '" << filename << "'\n\n";
return 0;
}
I am trying to concatenate some string but it works in one but not another.
Working: I take in 2 argument and then do this. a = hello, b = world
string concat = a + b;
The output would be hello world with no problem.
Not working: I read from file and concatenate with 2nd argument. assuming string from file is abcdefg.
string concat = (string from file) + b;
and it gives me worldfg.
Instead of concatenating, string from b overwrites the initial string.
I have tried a few other methods such as using stringstream but it doesn't work as well.
This is my code.
int main (int nArgs, char *zArgs[]) {
string a = string (zArgs [1]);
string b = string (zArgs [2]);
string code;
cout << "Enter code: ";
cin >> code;
string concat = code + b;
}
// The output above gives me the correct concatenation.
// If I run in command prompt, and do this. ./main hello world
// then enters **good** after the prompt for code.
// The output would be **goodworld**
However, I read some lines from the file.
string f3 = "temp.txt";
string r;
string temp;
infile.open (f3.c_str ());
while (getline (infile, r)) {
// b is take from above
temp = r + b;
cout << temp << endl;
}
// The above would give me the wrong concatenation.
// Say the first line in temp.txt is **quickly**.
// The output after reading the line and concatenating is **worldly**
Hope it gives more clear example.
Update:
I think I may have found out that the problem is due to the text file. I tried to create a new text file with some random lines inside, and it seem working fine. But if I try to read the original file, it gives me the wrong output. Still trying to put my head around this.
Then I tried to copied the content of the original file to the new file, and it seem to be working fine. Not too sure what is wrong here though. Will continue to test out, and hopefully it works fine.
Thanks for all the help! Appreciate it!
I get the same output as the chap who asked the original question:
$ ./a.out hello world
Enter code: good
goodworld
worldly
The problem here is the contents of the text file. For my example, the initial 7 characters in the text file are: "quickly". However, immediately following that are 7 backspace bytes (hex 08). This is what the contents looks like in emacs:
quickly^H^H^H^H^H^H^H
So how is this causing the mess?
Well the concatenation operation actually works correctly. If you do:
std::cout << "string length: " << temp.size() << "\n";
...you get the answer 19 which is made up of: "quickly" (7) + 7 backspace chars + "world"(5). The overwriting effect you observe is caused when you print this 19 char string to console: it is the console (eg xterm) that interprets the backspace sequence as meaning "move the cursor back to the left", thus removing earlier characters. If instead you pipe the output to file, you will see the full string (including the backspaces) is actually generated.
To get around this you might want to validate/correct the input that comes from the file. There are functions commonly available in C/C++ environments such as isprint(int c), iscntrl(int c) that you could make use of.
Update: as mentioned by another responder, other ASCII control characters will also have the same effect, eg, a carriage return (Hex 0D) will also move the cursor back to the left.
If I compile this
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
int main (int nArgs, char *zArgs[]) {
string a = string (zArgs [1]);
string b = string (zArgs [2]);
string code;
cout << "Enter code: ";
cin >> code;
string concat = code + b;
// The output above gives me the correct concatenation.
//However, I read some lines from the file.
ifstream infile;
string f3 = "temp.txt";
string r;
string temp;
infile.open (f3.c_str ());
while (getline (infile, r)) {
temp = r + code;
cout << temp << endl;
}
// The above would give me the wrong concatenation.
infile.close();
return 0;
}
it compiles and runs flawlessly. What does this do on your computer? If it fails, we may have to compare the contents of our temp.txt.
(This ought to be a comment rather than an answer, but it's too long. Sorry.)
I need to make a program in C++ that must read and write text files line by line with an specific format, but the problem is that in my PC I work in Windows, and in College they have Linux and I am having problems because of line endings are different in these OS.
I am new to C++ and don't know could I make my program able read the files no matter if they were written in Linux or Windows. Can anybody give me some hints? thanks!
The input is like this:
James White 34 45.5 10 black
Miguel Chavez 29 48.7 9 red
David McGuire 31 45.8 10 blue
Each line being a record of a struct of 6 variables.
Using the std::getline overload without the last (i.e. delimiter) parameter should take care of the end-of-line conversions automatically:
std::ifstream in("TheFile.txt");
std::string line;
while (std::getline(in, line)) {
// Do something with 'line'.
}
Here's a simple way to strip string of an extra "\r":
std::ifstream in("TheFile.txt");
std::string line;
std::getline(input, line));
if (line[line.size() - 1] == '\r')
line.resize(line.size() - 1);
If you can already read the files, just check for all of the newline characters like "\n" and "\r". I'm pretty sure that linux uses "\r\n" as the newline character.
You can read this page: http://en.wikipedia.org/wiki/Newline
and here is a list of all the ascii codes including the newline characters:
http://www.asciitable.com/
Edit: Linux uses "\n", Windows uses "\r\n", Mac uses "\r". Thanks to Seth Carnegie
Since the result will be CR LF, I would add something like the following to consume the extras if they exist. So once your have read you record call this before trying to read the next.
std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
If you know the number of values you are going to read for each record you could simply use the ">>" method. For example:
fstream f("input.txt" std::ios::in);
string tempStr;
double tempVal;
for (number of records) {
// read the first name
f >> tempStr;
// read the last name
f >> tempStr;
// read the number
f >> tempVal;
// and so on.
}
Shouldn't that suffice ?
Hi I will give you the answer in stages. Please go trough in order to understand the code.
Stage 1: Design our program:
Our program based on the requirements should...:
...include a definition of a data type that would hold the data. i.e. our
structure of 6 variables.
...provide user interaction i.e. the user should be able to
provide the program, the file name and its location.
...be able to
open the chosen file.
...be able to read the file data and
write/save them into our structure.
...be able to close the file
after the data is read.
...be able to print out of the saved data.
Usually you should split your code into functions representing the above.
Stage 2: Create an array of the chosen structure to hold the data
...
#define MAX 10
...
strPersonData sTextData[MAX];
...
Stage 3: Enable user to give in both the file location and its name:
.......
string sFileName;
cout << "Enter a file name: ";
getline(cin,sFileName);
ifstream inFile(sFileName.c_str(),ios::in);
.....
->Note 1 for stage 3. The accepted format provided then by the user should be:
c:\\SomeFolder\\someTextFile.txt
We use two \ backslashes instead of one \, because we wish it to be treated as literal backslash.
->Note 2 for stage 3. We use ifstream i.e. input file stream because we want to read data from file. This
is expecting the file name as c-type string instead of a c++ string. For this reason we use:
..sFileName.c_str()..
Stage 4: Read all data of the chosen file:
...
while (!inFile.eof()) { //we loop while there is still data in the file to read
...
}
...
So finally the code is as follows:
#include <iostream>
#include <fstream>
#include <cstring>
#define MAX 10
using namespace std;
int main()
{
string sFileName;
struct strPersonData {
char c1stName[25];
char c2ndName[30];
int iAge;
double dSomeData1; //i had no idea what the next 2 numbers represent in your code :D
int iSomeDate2;
char cColor[20]; //i dont remember the lenghts of the different colors.. :D
};
strPersonData sTextData[MAX];
cout << "Enter a file name: ";
getline(cin,sFileName);
ifstream inFile(sFileName.c_str(),ios::in);
int i=0;
while (!inFile.eof()) { //loop while there is still data in the file
inFile >>sTextData[i].c1stName>>sTextData[i].c2ndName>>sTextData[i].iAge
>>sTextData[i].dSomeData1>>sTextData[i].iSomeDate2>>sTextData[i].cColor;
++i;
}
inFile.close();
cout << "Reading the file finished. See it yourself: \n"<< endl;
for (int j=0;j<i;j++) {
cout<<sTextData[j].c1stName<<"\t"<<sTextData[j].c2ndName
<<"\t"<<sTextData[j].iAge<<"\t"<<sTextData[j].dSomeData1
<<"\t"<<sTextData[j].iSomeDate2<<"\t"<<sTextData[j].cColor<<endl;
}
return 0;
}
I am going to give you some exercises now :D :D
1) In the last loop:
for (int j=0;j<i;j++) {
cout<<sTextData[j].c1stName<<"\t"<<sTextData[j].c2ndName
<<"\t"<<sTextData[j].iAge<<"\t"<<sTextData[j].dSomeData1
<<"\t"<<sTextData[j].iSomeDate2<<"\t"<<sTextData[j].cColor<<endl;}
Why do I use variable i instead of lets say MAX???
2) Could u change the program based on stage 1 on sth like:
int main(){
function1()
function2()
...
functionX()
...return 0;
}
I hope i helped...
Please tell me what am I doing wrong here. What I want to do is this:
1.Having txt file with four numbers and each of this numbers has 15 digits:
std::ifstream file("numbers.txt",std::ios::binary);
I'm trying to read those numbers into my array:
char num[4][15];
And what I'm thinking I'm doing is: for as long as you don't reach end of files write every line (max 15 chars, ending at '\n') into num[lines]. But this somewhat doesn't work. Firstly it reads correctly only first number, rest is just "" (empty string) and secondly file.eof() doesn't seems to work correctly either. In txt file which I'm presenting below this code I reached lines equal 156. What's going on?
for (unsigned lines = 0; !file.eof(); ++lines)
{
file.getline(num[lines],15,'\n');
}
So the whole "routine" looks like this:
int main()
{
std::ifstream file("numbers.txt",std::ios::binary);
char numbers[4][15];
for (unsigned lines = 0; !file.eof(); ++lines)
{
file.getline(numbers[lines],15,'\n');// sizeof(numbers[0])
}
}
This is contents of my txt file:
111111111111111
222222222222222
333333333333333
444444444444444
P.S.
I'm using VS2010 sp1
Do not use the eof() function! The canonical way to read lines is:
while( getline( cin, line ) ) {
// do something with line
}
file.getline() extracts 14 characters, filling in num[0][0] .. num[0][13]. Then it stores a '\0' in num[0][14] and sets the failbit on file because that's what it does when the buffer is full but terminating character not reached.
Further attempts to call file.getline() do nothing because failbit is set.
Tests for !file.eof() return true because the eofbit is not set.
Edit: to give a working example, best is to use strings, of course, but to fill in your char array, you could do this:
#include <iostream>
#include <fstream>
int main()
{
std::ifstream file("numbers.txt"); // not binary!
char numbers[4][16]={}; // 16 to fit 15 chars and the '\0'
for (unsigned lines = 0;
lines < 4 && file.getline(numbers[lines], 16);
++lines)
{
std::cout << "numbers[" << lines << "] = " << numbers[lines] << '\n';
}
}
tested on Visual Studio 2010 SP1
According to ifstream doc, reading stops either after n-1 characters are read or delim sign is found : first read would take then only 14 bytes.
It reads bytes : '1' (the character) is 0x41 : your buffer would be filled with 0x41 instead of 1 as you seem to expect, last character will be 0 (end of c-string)
Side note, your code doesn't check that lines doesn't go beyond your array.
Using getline supposes you're expecting text and you open the file in binary mode : seems wrong to me.
It looks like the '\n' in the end of the first like is not being considered, and remaining in the buffer. So in the next getline() it gets read.
Try adding a file.get() after each getline().
If one file.get() does not work, try two, because under the Windows default file encoding the line ends with '\n\r\' (or '\r\n', I never know :)
Change it to the following:
#include <cstring>
int main()
{
//no need to use std::ios_base::binary since it's ASCII data
std::ifstream file("numbers.txt");
//allocate one more position in array for the NULL terminator
char numbers[4][16];
//you only have 4 lines, so don't use EOF since that will cause an extra read
//which will then cause and extra loop, causing undefined behavior
for (unsigned lines = 0; lines < 4; ++lines)
{
//copy into your buffer that also includes space for a terminating null
//placing in if-statement checks for the failbit of ifstream
if (!file.getline(numbers[lines], 16,'\n'))
{
//make sure to place a terminating NULL in empty string
//since the read failed
numbers[lines][0] = '\0';
}
}
}