I have a program in c++, during the program i use :
static ofstream s_outF(file.c_str());
if (!s_outF)
{
cerr << "ERROR : could not open file " << file << endl;
exit(EXIT_FAILURE);
}
cout.rdbuf(s_outF.rdbuf());
Meaning i redirect my cout to a file.
What would be the easiest way to return the cout back to the standard output?
thanks.
Save the old streambuf before you change cout's streambuf :
auto oldbuf = cout.rdbuf(); //save old streambuf
cout.rdbuf(s_outF.rdbuf()); //modify streambuf
cout << "Hello File"; //goes to the file!
cout.rdbuf(oldbuf); //restore old streambuf
cout << "Hello Stdout"; //goes to the stdout!
You can write a restorer to do that automatically as:
class restorer
{
std::ostream & dst;
std::ostream & src;
std::streambuf * oldbuf;
//disable copy
restorer(restorer const&);
restorer& operator=(restorer const&);
public:
restorer(std::ostream &dst,std::ostream &src): dst(dst),src(src)
{
oldbuf = dst.rdbuf(); //save
dst.rdbuf(src.rdbuf()); //modify
}
~restorer()
{
dst.rdbuf(oldbuf); //restore
}
};
Now use it based on scope as:
cout << "Hello Stdout"; //goes to the stdout!
if ( condition )
{
restorer modify(cout, s_out);
cout << "Hello File"; //goes to the file!
}
cout << "Hello Stdout"; //goes to the stdout!
The last cout would output to stdout even if condition is true and the if block is executed.
Related
Not easy to formulate that question, so I am sorry for any grief there..
I am writing to a csv file like this at the moment:
double indicators::SMACurrentWrite() {
if ( !boost::filesystem::exists( "./CalculatedOutput/SMAcurrent.csv" ) ) // std::cout << "Can't find my file!" << std::endl;
{
std::ofstream SMAfile;
SMAfile.open("./CalculatedOutput/SMAcurrent.csv");
SMAfile << "SMA" << endl << SMA[0] << endl; // .. or with '\n' at the end.
SMAfile.close();
}
else {
std::ofstream SMAfile;
SMAfile.open ("./CalculatedOutput/SMAcurrent.csv", ios::app); // Append mode
SMAfile << SMA[0] << endl; // Writing data to file
SMAfile.close();
}
return 0;
}
Each time the application runs, a new value is appended to the output file at the end:
SMA
32.325
I guess there is no way of just squeezing that new vector entry in there under the header( and over the number), but that is what I want to accomplish anyway.
So I guess I would have to read the existing output file back in,put it in a vector, and then replace the old file ? I started with smth like this:
double indicators::SMACurrentWrite() {
if ( !boost::filesystem::exists( "./CalculatedOutput/SMAcurrent.csv" ) ) // std::cout << "Can't find my file!" << std::endl;
{
std::ofstream SMAfile;
SMAfile.open("./CalculatedOutput/SMAcurrent.csv", ios::app);
SMAfile << "SMA" << endl << SMA[0] << endl; // .. or with '\n' at the end.
SMAfile.close();
}
else {
std::ofstream SMARfile("./CalculatedOutput/SMAReplacecurrent.csv");
std::ifstream SMAfile("./CalculatedOutput/SMAcurrent.csv");
SMARfile << SMA[0] << endl; // Writing data to file
SMARfile << SMAfile.rdbuf();
SMAfile.close();
SMARfile.close();
std::remove("./CalculatedOutput/SMAcurrent.csv");
std::rename("./CalculatedOutput/SMAReplacecurrent.csv","./CalculatedOutput/SMAcurrent.csv");
}
return 0;
}
...., but of course that just puts the new data in above the header like this :
32.247
SMA
32.325
..rather than this
SMA
32.247
32.325
I would rather this didn't become such a time- consuming exercise, but I appreciate any help on how I could get this done.
If you read in the first line from the input file you can use that to start the new file and it will leave the file pointer at the second line where the old data starts. Then you can write the new stuff like this:
if(!boost::filesystem::exists("./CalculatedOutput/SMAcurrent.csv"))
{
std::ofstream SMAfile;
SMAfile.open("./CalculatedOutput/SMAcurrent.csv", ios::app);
SMAfile << "SMA" << '\n' << SMA[0] << '\n';
SMAfile.close();
}
else
{
std::ofstream SMARfile("./CalculatedOutput/SMAReplacecurrent.csv");
std::ifstream SMAfile("./CalculatedOutput/SMAcurrent.csv");
// first read header from input file
std::string header;
std::getline(SMAfile, header);
// Next write out the header followed by the new data
// then everything else
SMARfile << header << '\n'; // Writing header
SMARfile << SMA[0] << '\n'; // Write new data after header
SMARfile << SMAfile.rdbuf(); // Write rest of data
SMAfile.close();
SMARfile.close();
std::remove("./CalculatedOutput/SMAcurrent.csv");
std::rename("./CalculatedOutput/SMAReplacecurrent.csv",
"./CalculatedOutput/SMAcurrent.csv");
}
IN IOS app, module written in C++ I am writing my data (map of basic strings and integers) to a text file. Using following method:
bool Recognizer::saveMap(const char * s)
{
if(trainingData.model && !trainingData.model.empty()) {
const string filename = string(s);
std::ofstream file(s, ios_base::trunc );
try{
if(! file.is_open())
{
file.open(s);
}
for (map<String,int>::iterator it=trainingData.idMap.begin(); it!=trainingData.idMap.end(); ++it)
{
cout << it->second << " " << it->first << endl;
file << it->first << endl << it->second << endl;
}
file.close();
}
catch(cv::Exception & e){
if(file.is_open())
file.close();
int code = e.code;
string message = e.err;
cerr << "cv::Exeption code: " << code << " " << message << endl;
return false;
}
std::streampos fileLength = iosFileSize(s);
cout << "Saved map to: " << filename << " length: " << fileLength << endl;
return true;
}
return false;
}
My contains one entry and console output indicates that two lines: string, string representing number have been written to my file.
Subsequent opening file for reading and reading using getline or using stream operator indicates that file is empty:
bool Recognizer::loadMap(const char * s)
{
std::streampos fileLenght = iosFileSize(s);
std::ifstream file(s, ios::in);
try{
if(file.is_open())
{
string name;
string lineName;
string lineTag;
int tag;
int count = 0;
while(getline(file,name))
{
if(getline(file,lineTag))
{
tag = stoi(lineTag,0,10);
count++;
cout << tag << " " << name << endl;
trainingData.idMap[name]=tag;
trainingData.namesMap[tag]=name;
}
}trainingData.personsCount=count;
file.close();
}
}
catch(cv::Exception & e){
if(file.is_open())
file.close();
int code = e.code;
string message = e.err;
cerr << "cv::Exeption code: " << code << " " << message << endl;
return false;
}
cout << "Loaded map from: " << s << " lenght: "<< fileLenght << endl;
return true;
}
I also copied from one of stackoverflow answers method returning file lenght and using it to verify lenghth of the file after write operation:
std::streampos iosFileSize( const char* filePath ){
std::streampos fsize = 0;
std::ifstream file( filePath, std::ios::binary );
fsize = file.tellg();
file.seekg( 0, std::ios::end );
fsize = file.tellg() - fsize;
file.close();
return fsize;
}
The file path passed to saveMap and loadMap seems to be legit. With path that the app could not write to, attempt to write caused exception.
There are no errors returned by write operation but both, attempts to read and iosFileSize() indicate that file is empty.
I am not sure if i need call file.open() and file.close() or file is open and closed automatically when output stream is created and later goes out of scope.
I experimented with those with the same result ( call to file.is_open returns true so the block calling file.open() is skipped.
What am I doing wrong?
I appreciate all responses.
It does not seem like you call file.flush(); anywhere in Recognizer::saveMap() after writing to the file stream. std::ofstream::flush() saves changes you've made to the file. Add file.flush(); between when you make changes to the code and when you close the file. See if that remedies your issue.
I also had the same issue. Using file.flush() everytime after you insert to a file can save your file.
However if you insert something like this, say,
file << "Insert This"; You will need to add file.flush().
But some people have issues, like if you just insert file << "Insert This" << endl; , this works fine. The key point here is that, std::endl calls flush() everytime it is used internally. you can say it is a shortend form of "\n" + flush().
I believe from looking at your code that you are overwriting your data when you open the file in the second program you should be using something like this.
std::fstream fs;
fs.open ("test.txt", ios::app)
instead of doing the ios::in
I've created a class which is supposed to read in DNA sequences: It contains an if stream private member:
Interface:
class Sequence_stream {
const char* FileName;
std::ifstream FileStream;
std::string FileFormat;
public:
Sequence_stream(const char* Filename, std::string Format);
NucleotideSequence get();
};
Implementation:
Sequence_stream::Sequence_stream(const char* Filename, std::string Format)
{
FileName = Filename;
FileStream.open(FileName);
FileFormat = Format;
std::cout << "Filestream is open: " << FileStream.is_open() << std::endl;
}
NucleotideSequence Sequence_stream::get()
{
if (FileStream.is_open())
{
char currentchar;
int basepos = 0;
std::string name;
std::vector<Nucleotide> sequence;
currentchar = FileStream.get();
if (currentchar == '>' && false == FileStream.eof()) { // Check that the start of the first line is the fasta head character.
currentchar = FileStream.get(); // Proceed to get the full name of the sequence. Get characters until the newline character.
while(currentchar != '\n' && false == FileStream.eof())
{
if (true == FileStream.eof()) {
std::cout << "The file ends before we have even finished reading in the name. Returning an empty NucleotideSequence" << std::endl;
return NucleotideSequence();
}
name.append(1, currentchar);
currentchar = FileStream.get();
} // done getting names, now let's get the sequence.
currentchar = FileStream.get();
while(currentchar != '>' && false == FileStream.eof())
{
if(currentchar != '\n'){
basepos++;
sequence.push_back(Nucleotide(currentchar, basepos));
}
currentchar = FileStream.get();
}
if(currentchar == '>')
{
FileStream.unget();
}
return NucleotideSequence(name, sequence);
} else {
std::cout << "The first line of the file was not a fasta format description line beginning with '>'. Are you sure the file is of FASTA format?" << std::endl;
return NucleotideSequence();
}
} else {
std::cout << "The filestream is not open..." << std::endl;
return NucleotideSequence();
}
}
However if I test it:
int main()
{
std::cout << "Let's try and read in a sequence!" << std::endl;
std::cout << "First we'll create a stream!" << std::endl;
Sequence_stream MyDNAStream("~/Dropbox/1_20dd5.fasta", "fasta");
std::cout << "Done!" << std::endl;
std::cout << "Now let's try and get a sequence!" << endl;
NucleotideSequence firstsequence = MyDNAStream.get();
return 0;
}
I see that the if stream is not open:
Let's try and read in a sequence!
First we'll create a stream!
Filestream is open: 0
Done!
The filestream is not open...
logout
[Process completed]
Although I thought the constructor function opens the if stream. What do I need to do to correct this so as the object is created and contains an open stream? (I know I'm yet to include a destructor which will close the stream upon destruction of the object).
Thanks,
Ben.
Your example shows that is_open returned false. I think you should check in your constructor that the file is indeed open, and throw if not.
In your case, I suspect this is due to passing "~/Dropbox/1_20dd5.fasta" as an input parameter. Did you test with a full pathname, with no ~? I have no knowledge of a C++ library that handles real path expansion (like python's os.path).
Redirecting cout or cerr to a file is easy enough. I can use this to redirect third party output to a file. However, after I have redirected the third party output to a file, how do I then use cout myself to output to the console?
I'm a great fan of RAII, so I once wrote this small helper class. It will redirect the stream until it goes out of scope, at which point it restores the original buffer. Quite handy. :)
class StreamRedirector {
public:
explicit StreamRedirector(std::ios& stream, std::streambuf* newBuf) :
savedBuf_(stream.rdbuf()), stream_(stream)
{
stream_.rdbuf(newBuf);
}
~StreamRedirector() {
stream_.rdbuf(savedBuf_);
}
private:
std::streambuf* savedBuf_;
std::ios& stream_;
};
Can be used like this:
using namespace std;
cout << "Hello stdout" << endl;
{
ofstream logFile("log.txt");
StreamRedirector redirect(cout, logFile.rdbuf());
cout << "In log file" << endl;
}
cout << "Back to stdout" << endl;
You save the buffer and restore it later:
std::streambuf *buf = std::cout.rdbuf(); //save
// Do other stuff
std::cout.rdbuf(buf); // restore
I'm basically trying to derive from wfilebuf so I can both output to a file and intercept the output to print it to the console/debug window as well as illustrated here:
http://savingyoutime.wordpress.com/2009/04/21/ and/or here: http://savingyoutime.wordpress.com/2009/04/22/40/
(ancient supporting ideas here: http://www.horstmann.com/cpp/streams.txt)
I've almost got it, but I can't seem to be able to both write to the underlying file AND peek at the input.
I overrode the sync() function similar to the second example but it seems that pbase() and pptr() are always NULL unless I set a buffer with setp(...), but this seems to break the file output. The file is always empty!
My crude attempt at this is below:
class LoggerBuffer : public wfilebuf {
// Functions
public:
LoggerBuffer();
~LoggerBuffer();
void open(const wchar_t loggerFile[]);
void close();
int sync();
int_type overflow(int_type c = EOF);
void setState(int newState);
// Variables
private:
int currentState;
static const int BUFFER_SIZE = 10;
wchar_t buffer[BUFFER_SIZE];
};
class LoggerStream : public wostream {
// Functions
public:
LoggerStream();
~LoggerStream();
void open(const wchar_t loggerFile[] = 0);
void close();
void setState(int newState);
};
LoggerBuffer::LoggerBuffer() {
wfilebuf::open("NUL", wios::out); currentState = 1;
}
LoggerBuffer::~LoggerBuffer() {
wcout << "Destruction of LoggerBuffer" << endl;
}
void LoggerBuffer::open(const wchar_t loggerFile[]) {
wcout << "LoggerBuffer Opening " << loggerFile << endl;
close();
wfilebuf* temp = wfilebuf::open(loggerFile, wios::out); //ios::out | ios::app | ios::trunc
setp (buffer, buffer+(BUFFER_SIZE-1));
}
void LoggerBuffer::close() {
wfilebuf::close();
}
int LoggerBuffer::sync() {
wcout << " Syncing ";
int out_waiting = pptr() - pbase();
wcout << out_waiting << " characters!";
wcout << endl;
wcout << "pptr(): " << (unsigned int)pptr() << endl;
return wfilebuf::sync();
}
LoggerBuffer::int_type LoggerBuffer::overflow(int_type c) {
wcout << "overflow! (" << (wchar_t)c << ")" << endl;
if (c == EOF)
return EOF;
if (sync() == EOF)
return EOF;
return wfilebuf::overflow(c);
}
void LoggerBuffer::setState(int newState) {
wcout << "New buffer state = " << newState << endl;
currentState = newState;
}
LoggerStream::LoggerStream() : wostream(new LoggerBuffer), wios(0) {
}
LoggerStream::~LoggerStream() {
delete rdbuf();
}
void LoggerStream::open(const wchar_t loggerFile[]) {
wcout << "LoggerStream Opening " << loggerFile << endl;
((LoggerBuffer*)rdbuf())->open(loggerFile);
}
void LoggerStream::close() {
((LoggerBuffer*)rdbuf())->close();
}
void LoggerStream::setState(int newState) {
wcout << "New stream state = " << newState << endl;
((LoggerBuffer*)rdbuf())->setState(newState);
}
Full disclosure: I asked a question regarding something similar earlier: Simple wostream logging class (with custom stream manipulators)
I think I have solved that problem though.
Any help is greatly appreciated! Thanks!
I'd use a filtering streambuf, that does no buffering of its own, instead passing data through to a real streambuf (i.e., one that does real buffering) for each of the destinations. This should simplify your code quite a bit and let you concentrate on the parts you really care about.