how to open file from c++

[marvin77]

guys, how to open file from c++
this is my coding, can you help me to fix it??

 	{
		cout<<"Find subject that you want: "<<endl;
		cin>>b;
		strcat("D:/TUGAS/1/1",b);
		ifstream data;
		data.open(b);
		while(data)
		{
			data.getline(b,sizeof(b));
			cout<<b<<endl;
		}
		data.close();
	}
	system("pause");
}

if i execute it, it always can't open the file...

[MiiNiPaa]

1) if your files will be in program execution folder, there is no need to specify full path.
2) strcat("D:/TUGAS/1/1",b); You cannot do that. It will try to append b string to const literal, what is forbidden but will work because of compatibility conversion to char* (Should give you a warning).
3) Even it it would work, you forgot another slash at the end of line, so if you enter "test", you wil be trying to open "D:/TUGAS/1/1test"

[marvin77]

so the strcat("D:/TUGAS/1/1",b); won't work? what the solution for this? must we replace the code?

[MiiNiPaa]

If file in same folder your program is, you can use just:

std::cin >> b;
std::istream data(b);

If not:

char path[40] = "D:/TUGAS/1/1/"; //Copies string into array.
char fliename[20];
std::cin >> filename;
std::strncat(path, filename, 20);
std::ifstream data(path);

[Rechard3]

here's something about windows:
1)- windows -unlike linux- uses a backslash, not a slash.
2)- and in c++, you can't write a backslash directly, to write a backslash in a string literal you should write two backslashes.
replace line 6 with this:

data.open("D:\\TUGAS\\1\\1");

i think that would work.

[MiiNiPaa]

windows -unlike linux- uses a backslash, not a slash.

From at least Vista it supports forward slashes internally.

[marvin77]

{
		char path[40] = "D:\\TUGAS\\1\\1\\"; //Copies string into array.
		char filename[20];
		cout<<"Masukkan nama mata kuliah yang dicari: "<<endl;
		cin >> filename;
		strncat(path, filename, 20);
		ifstream data(path);
		data.open("D:\\TUGAS\\1\\1\\");
		while(data)
		{
			data.getline(b,sizeof(b));
			cout<<b<<endl;
		}
		data.close();
	}
	system("pause");
}

ehm, it's not wrong, but the file just can't open... -___-" i'm so confused

[MiiNiPaa]

		ifstream data(path);
		data.open("D:\\TUGAS\\1\\1\\");//Terribly wrong. Do not do this. 

Also if you want to use backslashes, use raw string literals:

char path[40] = R"(D:\TUGAS\1\1\)"; //Copies string into array.
char fliename[20];
std::cin >> filename;
std::strncat(path, filename, 20);
std::ifstream data(path);
while(data.getline(b,sizeof(b))) { 
    std::cout<<b<<endl;
}

[marvin77]

{
		char path[40] = "(D:\TUGAS\1\1\)"; 
		char filename[20];
		cout<<"find subject: "<<endl;
		cin >> filename;
		strncat(path, filename, 20);
		ifstream data(path);
		while(data.getline(b,sizeof(b)))
		{ 

			cout<<b<<endl;}

		data.close();
	}
	system("pause");
}

guys, it's the same work, but the file can't open, i'm hopeless T_T

[MiiNiPaa]

Does such file exist?
Show a screenshot of that folder.
What do you input exactly?
You do not forget file extension, do you?

[marvin77]

i give you my full code, sorry if it's in my language

#include <iostream>
#include <fstream>
#include <string.h>

using namespace std;

int maen()
{
	ofstream myfile;
	myfile.open("Algolanjut.txt");
	myfile<<"NIM		Nama		Program Studi	Tugas		UTS		UAS		TOTAL	HURUF	"<<endl;
	myfile<<"============================================================================================================="<<endl;
	myfile<<"535050056	Budi		TI		90		80		70		77	B	"<<endl;
	myfile<<"535090065	Wati		TI		100		100		99		99.5	A	"<<endl;
	myfile<<"835100077	Tina		SI		90		70		50		64	C	"<<endl;
	myfile.close();
	return 0;
}

void main()
{
	char b[30], c[30],nama[30];
	int a;
	cout<<" 1. Menambah mata kuliah baru " <<endl;
	cout<<" 2. Mencari mata kuliah " <<endl;
	cout<<" Masukkan input 1 atau 2 : ";
	cin>>a;
	if (a==1)
	{	
		cout<<"Masukkan nama mata kuliah baru: "<<endl;
		cin>>c;
		ofstream myfile;
		myfile.open(strcat(c,".txt"));
		myfile.close();
	}
	if (a==2)
	{
		char path[40] = "(D:\TUGAS\1\1\)"; //Copies string into array.
		char filename[20];
		cout<<"Masukkan nama mata kuliah yg dicari: "<<endl;
		cin >> filename;
		strncat(path, filename, 20);
		ifstream data(path);
		while(data.getline(b,sizeof(b)))
		{ 

			cout<<b<<endl;}

		data.close();
	}
system("pause");
}

try my coding

[MiiNiPaa]

char path[40] = R"(D:\TUGAS\1\1\)";
char path[40] = "(D:\TUGAS\1\1\)";

Find the difference

Also show how you call your file and what file you actually have. I'm supposing you are not providing file extension.

[kbw]

Don't call open/close on a stream.
You specify \ in a string literal with \\
Use std::string when you need a string.

Applying those, that code becomes:

{
	std::string path = "D:\\TUGAS\\1\\1\\"; 
//	std::string path = "D:/TUGAS/1/1/";  // or this 
	std::string filename;
	std::cout<<"find subject: ";
	std::cin >> filename;
	path += filename;

	std::string line;
	ifstream data(path);
	while (std::getline(data, line))
		std::cout << line << std::endl;

	system("pause");
}

[marvin77]

what the use of "R", if i add it, the program error, it's say call 1 or 2, if i call 2, we type the file that we search, if it in the folder, the file will open, if not, then it's end of program

[MiiNiPaa]

what the use of "R", if i add it, the program error

Oh, you have an outdated compiler which doesn't support C++11.
Ok, use "D:\\TUGAS\\1\\1\\"
I want to see, what exactly you are typing, and screenshot of folder with actual files.
Example
I am typing "Velocities.xls"
My folder looks like http://gm4.in/i/du0.png

[marvin77]

kbw, it won't work --"

{
	std::string path = "D:/TUGAS/1/1/"; 
	std::string filename;
	std::cout<<"find subject: ";
	std::cin >> filename;
	path += filename;

	std::string line;
	ifstream data(path);
	while (std::getline(data, line))
		std::cout << line << std::endl;

	system("pause");
}

[marvin77]

http://imageshack.us/photo/my-images/571/20696473.png/
that's my file, i want to open kalku or kalku2, but it become
http://imageshack.us/photo/my-images/443/97196496.png/

but the kalku or kalku2 text document, won't open.

[MiiNiPaa]

As I supposed you are missing extension. It is actually kalku.txt . Windows hides it by default, but it is still part of the file.
http://windows.microsoft.com/en-in/windows-vista/show-or-hide-file-name-extensions

[kbw]

kbw, it won't work --"

Why do you say that?

[marvin77]

kbw, beacuse the program can't open the file
thanks to MiiNiPaa, you really help me, but the file still can't open,thank you :')