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Thread: fstream -> stdout

  1. #1
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    Default fstream -> stdout

    HI all!
    I have ofstream objects.
    Some times i need write throu tihis objects into stdout.
    How i can relese that?

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    Default Re: fstream -> stdout

    Use std::cout. It is a stream interface to stdout (include <iostream>).

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    Default Re: fstream -> stdout

    No no no
    i hope in code language i can explain my problem better...

    Qt Code:
    1. // global variable
    2. ofstream gl_fileLog;
    3.  
    4. int main(int argc, char *argv[])
    5. {
    6. // if program run with param - it log file path
    7. // else log must write into stdout
    8. if ( argc > 1)
    9. gl_fileLog.open( "some_name", ios::app );
    10. else
    11. //..... em now i want that in future my gl_FileLog write into stdout
    12. }
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    gl_fielLog i use in 5 other classes, and i dont want always write 2 variants.
    Last edited by zlatko; 21st January 2006 at 13:04.

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    Default Re: fstream -> stdout

    My answer still stands

    Change:
    Qt Code:
    1. ofstream gl_fileLog;
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    to
    Qt Code:
    1. ostream gl_fileLog;
    To copy to clipboard, switch view to plain text mode 

    And assign cout to it if you want to log into stdout or your ofstream object otherwise (it is possible that gl_fileLog has to be a reference, I don't know how will cout behave if you attempt to copy it).

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    Default Re: fstream -> stdout

    My question also still stands too

    hm..with stdio it relized simply

    Qt Code:
    1. FILE *m_fileLog;
    2. ...
    3. if ( !m_bConsoleMode )
    4. {
    5. if ( ( m_fileLog = fopen( "/usr/local/mhat-1.0a/var/log/mhatControl.log","a" ) ) == NULL )
    6. exit( 0 );
    7. }
    8. else
    9. m_fileLog = stdout;
    10.  
    11. // write in file or in stdout
    12. fprintf(m_fileLog,"HELLO");
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    With stdio, when i print message i didnt must do any choices....with ostream i see i must do choise always...or i cant understand how i must solve it

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    Default Re: fstream -> stdout

    I really answered your question already

    Qt Code:
    1. class logClass{
    2. public:
    3. logClass(ostream &str) : m_str(str){ m_str.open(ios::append); };
    4. logString(std::string &s){ m_str << s << std::endl; }
    5. protected:
    6. ostream &m_str;
    7. };
    8.  
    9. ofstream somefile("logme.txt");
    10.  
    11. void initialise(bool usestdout){
    12. logClass *log = new logClass(usestdout ? std::cout : somefile);
    13. log->logString("testing");
    14. }
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    Default Re: fstream -> stdout

    I understand now. Ok Thanks i'll try it

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    Default Re: fstream -> stdout

    A slightly different solution is to use rdbuf() to redirect the output:

    Qt Code:
    1. #include <iostream>
    2. #include <fstream>
    3.  
    4. int main(int argc, char** argv)
    5. {
    6. std::ofstream logFile;
    7.  
    8. // output will initially go to stdout
    9. std::ostream logStream(std::cout.rdbuf());
    10.  
    11. if( argc > 1 )
    12. {
    13. // open log file
    14. logFile.open("log.txt");
    15.  
    16. // redirect output to our log file
    17. logStream.rdbuf(logFile.rdbuf());
    18. }
    19.  
    20. logStream << "Hello world!" << std::endl;
    21.  
    22. return 0;
    23. }
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  9. #9
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    Talking Re: fstream -> stdout

    Quote Originally Posted by wysota
    I really answered your question already

    Qt Code:
    1. class logClass{
    2. public:
    3. logClass(ostream &str) : m_str(str){ m_str.open(ios::append); };
    4. logString(std::string &s){ m_str << s << std::endl; }
    5. protected:
    6. ostream &m_str;
    7. };
    8.  
    9. ofstream somefile("logme.txt");
    10.  
    11. void initialise(bool usestdout){
    12. logClass *log = new logClass(usestdout ? std::cout : somefile);
    13. log->logString("testing");
    14. }
    To copy to clipboard, switch view to plain text mode 
    hoho, your code's ill-formed, you really should not initialize a reference in the initialization list
    1. Users don't have the manual, and if they did, they wouldn't read it.
    2. In fact, users can't read anything, and if they could, they wouldn't want to.

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    Default Re: fstream -> stdout

    Quote Originally Posted by bood
    hoho, your code's ill-formed, you really should not initialize a reference in the initialization list
    So what is a "healthy" way to initialise a member reference? And what is "ill" about my approach?

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    Default Re: fstream -> stdout

    @bood
    AFAIK there is only and only one way to initialize member references here: in the constructor init list. If you try it in the body of the ctor it's not an initialization but an assignment! There's only a little problem - which variable are you assigning that value?

  12. #12
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    Unhappy Re: fstream -> stdout

    Quote Originally Posted by wysota
    So what is a "healthy" way to initialise a member reference? And what is "ill" about my approach?
    Sorry, my mistake
    I misunderstood the standard...
    1. Users don't have the manual, and if they did, they wouldn't read it.
    2. In fact, users can't read anything, and if they could, they wouldn't want to.

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