ifstream myfile;
myfile.open("FileTest");
string line;
if(myfile.is_open())
{
cout<<"Reading from file...";
getline(myfile,line);
}
if(myfile.fail())
{
cout<<"Unable to open file"<<endl;
}
myfile.close();
C++ tries to open the file in the current directory with the exact name FileTest. Check to see if the file is in the current directory? Maybe you spelled the name incorrectly? Maybe you forgot to write FileTest.txt? You are using ifstream, which will fail if the file you're trying to open does not exist or is corrupted.
Related
I am trying to read about 2 lines from a file of text into a std::string in c plus plus. I have looked through several answers and found none that work on my device. Can anyone tell me what I am doing wrong? The method is currently returning a null string, and doesn't correctly open the file or read it at all.
std::string readFile(std::string filename) {
std::ifstream infile;
infile.open(filename);
std::string output;
if (infile.is_open()) {
while(infile.good()) {
infile >> output;
}
}
infile.close();
return output;
}
Not sure what file you are trying to open but that's a completely separate problem. The code you've written will open a file if you give it a path to a file that it can open. Check your current working directory and confirm the path is correct.
Even after you solve that problem, you're going to have more problems though.
I expect that you are confused because you are repeatedly overwriting output with this line:
infile >> output;
perhaps you meant to declare output as a std::stringstream
And for me it doesn't return an empty string, it returns the last word of the file. I guess it depends what's in your file.
I am trying to open a file where the file path is taken as a user input.
However, the C++ runtime says that the file does not exist, but when I hardcode the string, I am able to open the file.
std::shared_ptr<Task> Daemon::create_new_task(string &location){
std::ifstream file;
std::cout<<"Create new task->"<<location<<endl;
file.open(location.c_str(), std::ios::in);
if (!file.is_open())
perror("Error");
boost::filesystem::path f("<filepath>");
std::cerr<<boost::filesystem::exists(f);
std::stringstream buf;
buf << file.rdbuf();
return std::make_shared<Task>(location,buf.str());
}
perror() says file not found, while the second output is 1.
I tried absolute and relative paths. None of them work.
Any thoughts on this?
Can anyone tell me what is wrong with this code? I always get not open.
#include <iostream>
#include <fstream>
using namespace std;
int main(){
fstream fs;
fs.open("fsfile2",ios::in|ios::out|ios::binary);
if(fs.is_open()){
fs.write("wow",sizeof("wow"));
char str[20];
fs.read((char*)str,sizeof(str));
cout<<str<<endl;}
else
cout<<"Not open\n";
return 0;
}
Try this code
fs.open("fsfile2", ios::app|ios::in|ios::out|ios::binary);
By using the open() like you are that file will not be created if that is your goal.
If you want to create a new file please look at: fstream won't create a file
If the file exists, you are not looking for it in the right path. Or change the file name to the full path or put the executable in the folder where the file is.
Hope this helps.
Probably, you do not have permissions to create files in the directory, where your executable is.
Solution:
Please add a file extension to the filename.
If it's a text file, it will be
"fsfile2.txt"
Then, I tried removing
ios::in
since the first process only writes to file, and by removing that, the file is created and "wow" is also written at it.
In order for these lines
fs.read((char*)str,sizeof(str));
cout<<str<<endl;
to work,
You need to close the stream after writing to it, then open the stream in read mode, then read the contents. Take note that closing the stream will save the edited file.
Additional:
You can also change
fs.write("wow",sizeof("wow"));
to
fs << "wow";
You can do the same when reading from file,
fs >> str;
You can also use the string class of C++, instead of char array so that the number of characters inside the file won't be your problem anymore.
#include <string>
string str;
Checking for EOF (end-of-file) is recommended since files are read line by line. Once you add a new line and add a character to the line, the code that doesn't loop until EOF will only read the first line of the file.
In order to solve this, it is recommended to loop until EOF is reached.
while(!fs.eof()) {
fs >> str;
cout << str << endl;
}
So here is the improved snippet:
#include <string>
fs.open("fsfile2.txt", ios::out); // ios::out for write only
if(fs.is_open()) {
// writes "wow" to file
fs << "wow";
// closes the file
fs.close();
// ios::in for read only
fs.open("fsfile2.txt", ios::in);
// better to define variable just before using it
string str;
// loops until end-of-file
while(!fs.eof()) {
// reads a line from file, stores it to str
fs >> str;
// shows str to screen
cout << str << endl;
}
}
*Note: I removed
ios::binary
Since your code is not dealing with binary files yet.
I tried these and it worked fine! Have a nice day!
fstream fs; does not create a new file for you.
You need to make sure that the file exists in your project directory.
On the other hand, if you were to use ofstream fs("file.txt"); it would create the file for you. Or use only ios::out when you open fstream fs, this will create the file for you.
I am using Visual Studio 2013
So I have to open a .ppm image file and do some work on it, but the ifstream I'm trying to use to read the data fails to open the image file. I am pretty sure the image file is in the working directory (I have created and read some simple .txt files to make sure). And even after excessive research I can't figure out what is going on.
Here's the relevant code
EDIT: I added some more code to get an idea of what I'm trying to do
Image * PPMImageReader::read(std::string filename){
std::string line;
int width, height, max_val;
std::ifstream src(filename, std::ios_base::binary);
if (src.fail()) { //failbit is always set but not badbit
perror("Logical error on i/o operation. failbit was set\n");
if (src.bad())
perror("Read/writing error on i/o operation. badbit was set");
}
if (!src.is_open()) { //and of course this return true
printf("File was not opened\n");
exit(1);
}
//Edited
getline(src, line, '\n');
if (line.empty())
getline(src, line);
if (line.find("P6") == std::string::npos) {
printf("wrong format\n");
exit(1);
}
As from discussed came to know the problem is relative path.
fstream support relative paths as below..
Consider the following case where your input file is one level up than exe file.
E:\MyProgramBin\YourExe.exe
E:\YourInputFile.ppm
In this case, you can create your filename as below.
filename1 = "..\YourInputFile.ppm"
and use that filename1 in ifstream
std::ifstream src(filename1, std::ios_base::binary);
On Windows, I have no problems opening the file from string. On Linux (where it needs to work) I can't open the file.
string name;
//open 1st file, with the next file name - this works
fstream file( "data.dat", ios::in);
if(file.good()){
getline(file, name);
//some code here
file.close();
}else{
return 1;
}
// this here does not work
fstream file1(name.c_str() , ios::in);
if(file1.good()){
//some code here
file1.close();
}else{
cout<<"can't open file"<<endl;
return 1;
}
If instead name.c_str() I write the file name directly it works, but every try on getting the name from the file ended with the file not opening.
I've tried creating const char* from name, doesn't work too.
The file probably has Windows-style line endings. Either sanitise the file, or check for and remove any carriage-return character, \r, at the end of each line.