so i am working on something and i cant seem to get why it isn't working.
void display_alls()
{
ifstream fpd;
fpd.open("student2.txt",ios::in);
if(!fpd)
{
cout<<"ERROR!!! FILE COULD NOT BE OPEN ";
getch();
return;
}
while(fpd)
{
int pos;
string seg;
cout<<"\tUSN"<<setw(10)<<"\tName"<<setw(20)<<"Book Issued\n";
//fp.seekg(pos,ios::beg);
getline(fpd,st.usn,'|');
getline(fpd,st.name,'|');
getline(fpd,st.email,'|');
getline(fpd,st.phone,'|');
getline(fpd,st.stbno,'|');
getline(fpd,seg);
cout<<"\t"<<st.usn<<setw(20)<<st.name<<setw(10)<<st.stbno<<endl;
}
fp.close();
}
[Error] D:\library\library_v1.cpp:514: error: no matching function for
call to `getline(std::ifstream&, char[20], char)'
error is on each line with getline! but not in "getline(fpd,seg);"
this thing isn't working on MingW compiler but was working on my college system, idk maybe they are having older compiler, can you please tell me what is wrong.
much appreciated.
The error message suggests that the code is attempting to read into an array of 20 characters. Unfortunately std::getline does not deal in character arrays. It only reads into std::string, which is why it works with string seg; For character arrays you need to use std::istream::getline. Link to documentation page
However life will probably be easier for you if you can replace the character arrays in the data structure with std::strings.
std::getline, if that's what you're trying to use, is defined in the <string> header. You will want to include it:
#include <string>
Then you can call it via std::getline. If you get tired of typing std::, you can do:
using namespace std;
Depending on the IDE or build setup, these things can sometimes be done for you already. It's possible that is why this works on the school computer, but not yours.
Related
I am beginner in C++ and I have a question that is beyond my limits.
I compile under GNU GCC.
I use
#include<stdio.h>
also known as:
#include<cstdio>
At some point in my program I tell the program to use the file de_facut.txt as an in file:
freopen("de_facut.txt","r",stdin);
How can I tell the program to use the console to put the input (as default) instead of the in file?
First I want to read from that file, but later in the program I want the user to enter input in the console.
I hope you understood my problem, I am not very good at english.
The same question has been asked about stdout: How to redirect the output back to the screen after freopen("out.txt", "a", stdout), but the answer is the same for both - there's no clean way of doing this: http://c-faq.com/stdio/undofreopen.html
Since you do need to read from the console later in the program, I'd suggest you just open the file as, well, a file. If the reason you wanted to use stdin to read from a file is the convenience of not having to pass the file handle to functions like fscanf, you could consider using fstream facilities instead - the code can look exactly as when reading from the console:
#include <iostream>
#include <fstream>
using namespace std;
int main()
{
int x;
cin >> x; // reading from console
{
ifstream cin("input.txt");
cin >> x; // reading from file
}
cin >> x; // again from console
return 0;
}
Use fclose():
FILE *fp=freopen("data.txt","r",stdin);
/*your code here*/
fclose(fp);
ref: C library function - freopen()
In windows,
freopen("CON","r",stdin);
this code worked for me. It switches the stdin to console.
P.S: The text file used to take input before this, must be ended with a newline.
The program almost runs but i am not sure how to make the .txt file for this , its not giving me an error.
the project asks me to:
" File encryption is the science of writing the contents of a file in a secret code. Your encryption program should work like a filter, reading the contents of one file, modifying
the data into a code, and then writing the coded contents out to a second file.
The second file will be a version of the first file, but written in a secret code. Although there are complex encryption techniques, you should come up with a simple one of your own. For example, you could read the first file one character at a time, and add 10 to the ASCII code of each character before it is written to the second file. "
#include <iostream>
#include <fstream>
using namespace std;
int main()
{
char ch;
fstream fin, fout;
fin.open("testone.txt", ios::in);
fout.open("encrypted.txt", ios::out);
while (!fin.eof())
{
fin.get(ch);
fout.put(ch + 10);
}
fin.close();
fout.close();
system("pause");
return 0;
}
Read this -
Error LNK1561: entry point must be defined
https://social.msdn.microsoft.com/Forums/vstudio/en-US/e1200aa9-34c7-487c-a87e-0d0368fb3bff/error-lnk1561-entry-point-must-be-definedproblem-in-c?forum=vclanguage
Not up on my Visual C, but you may need #include <cstdlib> to get system
LNK1561 means your main function can't be found. Clearly the main function is present, so this should compile. Follow Beta's suggestion and ensure you can compile and run a trivial program.
Putting Compiling issues aside, This code won't work.
Overarching Problem: You are not checking for any errors along the way, so there is no way for your program to tell if anything has gone wrong.
For example, what if the file didn't open? The while (!fin.eof()) becomes an infinite loop. If the file is not open, you can never read EOF. Trying to use EOF as a loop condition is a bad idea anyway. Definitely read the link in #Steephen's comment.
If you fail to read a character with fin.get(ch); then what? The current code tries to use the character anyway. Bad idea.
Testing a stream is pretty simple. if (!fin) does the job. Read up on how streams work to learn why. Thius simple test doesn't tell you what went wrong, but at least you know something went wrong.
To make things easier, most stream functions return the stream. This lets you chain stream operations together and makes if (!fin.get(ch)) an easy way to tell if get worked.
So your IO loop can be as simple as
while (fin.get(ch) && fout.put(ch + 10))
{
}
If get couldn't get ch for any reason--unopened file, end of file, unreadable file--the while loop exits. Afterwards you can query fin to find out why. If EOF, awesome. If not EOF, the output file's probably wrong.
The same applies to put. If put failed, the loop ends. Test for why and decide if you want to keep the file.
I also recommend dropping a quick test at the end of main to print out a check.
fin.open("encrypted.txt", ios::in);
while (fin.get(ch) && std::cout.put(ch - 10))
{
}
A better test would be to read the character, undo the encryption, and compare against the original input.
I am writing an algorithm that wants to check if google-chrome or has the same version as the input given by the user. for that I need a way to check what version google-chrome has. I am using a linux machine to program but I want to make it work at home where I use win 8.1
Is there a way to check in C/C++ what the version of a program is?
I thing it is best to get the awnser in a string because then i can just compare with
if(strcmp(version, input)=1)
Thanks for reading.
PS. I started in C++ but I can change, even to java if neccesary
here is the basic version of what i have now:
#include <iostream>
#include <string>
using namespace std;
#define x 256;
int main(){
std::string version;
std::string input;
//get version
if(strcmp(version, input)=1){
//versions are equal
}
//chrome needs to be updaded
return 0;
}
You can launch a terminal process from C with the popen() command. You'll need to include the stdio.h header. Here's a code snippet that might help you:
FILE *pd = popen("google-chrome --version", "r");
char output[50];
fgets(output,50,pd);
pclose(pd);
In the output array you'll get something like "Google Chrome 25.0.1364.97"
Just like the title says, I've been working on a fairly large program and have come upon this bug. I'm also open to alternatives for searching a file for a string instead of using . Here is my code narrowed down:
istreambuf_iterator<char> eof;
ifstream fin;
fin.clear();
fin.open(filename.c_str());
if(fin.good()){
//I outputted text to a file to make sure opening the file worked, which it does
}
//term was not found.
if(eof == search(istreambuf_iterator<char>(fin), eof, term.begin(), term.end()){
//PROBLEM: this code always executes even when the string term is in the file.
}
So just to clarify, my program worked correctly in Linux but now that I have it in a win32 app project in vs2010, the application builds just fine but the search function isn't working like it normally did. (What I mean by normal is that the code in the if statement didn't execute because, where as now it always executes.)
NOTE: The file is a .xml file and the string term is simply "administration."
One thing that might or might not be important is to know that filename (filename from the code above) is a XML file I have created in the program myself using the code below. Pretty much I create an identical xml file form the pre-existing one except for it is all lower case and in a new location.
void toLowerFile(string filename, string newloc, string& newfilename){
//variables
ifstream fin;
ofstream fout;
string temp = "/";
newfilename = newloc + temp + newfilename;
//open file to read
fin.open(filename.c_str());
//open file to write
fout.open(newfilename.c_str());
//loop through and read line, lower case, and write
while (fin.good()){
getline (fin,temp);
//write lower case version
toLowerString(temp);
fout << temp << endl;
}
//close files
fout.close();
fin.close();
}
void toLowerString(string& data){
std::transform(data.begin(), data.end(), data.begin(), ::tolower);
}
I'm afraid your code is invalid - the search algorithm requires forward iterators, but istreambuf_iterator is only an input iterator.
Conceptually that makes sense - the algorithm needs to backtrack on a partial match, but the stream may not support backtracking.
The actual behaviour is undefined - so the implementation is allowed to be helpful and make it seem to work, but doesn't have to.
I think you either need to copy the input, or use a smarter search algorithm (single-pass is possible) or a smarter iterator.
(In an ideal world at least one of the compilers would have warned you about this.)
Generally, with Microsoft's compiler, if your program compiles and links a main() function rather than a wmain() function, everything defaults to char. It would be wchar_t or WCHAR if you have a wmain(). If you have tmain() instead, then you are at the mercy of your compiler/make settings and it's the UNICODE macro that determines which flavor your program uses. But I doubt that char_t/wchar_t mismatch is actually the issue here because I think you would have got an warning or error if all four of the search parameters didn't use the same the same character width.
This is a bit of a guess, but try this:
if(eof == search(istreambuf_iterator<char>(fin.rdbuf()), eof, term.begin(), term.end())
I have recently begun to experiment with winapi in C++. Coming along nicely so far.
I do however having a problem with finding a way to read the first line of a file, and displaying it in a textbox.
After some google searching it seems that some people suggest using winapis functions for this, while other say that using fstream is simpler. I did go the fstream way but i run in to some trouble, probably nothing very difficult but, i cannot find an answer for it!
this is my code:
string line;
ifstream filen ("tid.txt");
if (filen.is_open())
{
getline (filen,line);
cout << line << endl;
filen.close();
}
SetDlgItemText(hwnd, IDC_MAIN_EDIT, line);
This give me this problem from the compiler:
Cannot convert `std::string' to `const CHAR*'
Need somekind of conversion here, but dont know what.
What do you think?
Try this:
SetDlgItemText(hwnd, IDC_MAIN_EDIT, line.c_str());