copying a file

This is a discussion on copying a file within the C Programming forums, part of the General Programming Boards category; I want to read the filename that is data in one file and open that filename specified as data. say, ...

  1. #1
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    copying a file

    I want to read the filename that is data in one file and open that filename specified as data.

    say, file1="filetoread";
    file2="filetowriteto";

    I want to read the data from file1 (say line 1 of file1 is "c:\myfile.txt"), then I want to open the file listed on line 1 of file1 and copy the data from c:\myfile.txt to file2.

  2. #2
    and the hat of wrongness Salem's Avatar
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    Try a board search
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  3. #3
    Guest Sebastiani's Avatar
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    Post the code you attempted to do this with.
    Code:
    #include <cmath>
    #include <complex>
    bool euler_flip(bool value)
    {
        return std::pow
        (
            std::complex<float>(std::exp(1.0)), 
            std::complex<float>(0, 1) 
            * std::complex<float>(std::atan(1.0)
            *(1 << (value + 2)))
        ).real() < 0;
    }

  4. #4
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    This is what I have so far:
    It works up to: " if ((fnewsource = fopen(sourcefile,"r"))==NULL)"...it's not able to open the file.

    see the attached file...
    Attached Files Attached Files

  5. #5
    Just Lurking Dave_Sinkula's Avatar
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    Code:
    fgets(fileName,256,fold);
    sourcefile=fileName;
    /* ... */
    if ( (fnewsource = fopen(sourcefile,"r"))==NULL )
    If you don't pick off the '\n' that fgets may leave in, it's still there. So if you are intending to open "file.txt", you may be trying to open "file.txt\n". More info.
    7. It is easier to write an incorrect program than understand a correct one.
    40. There are two ways to write error-free programs; only the third one works.*

  6. #6
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    Thanks. I will try that and get back to you.

  7. #7
    Guest Sebastiani's Avatar
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    fgets() retrieves and stores the newline in the buffer - you have to strip it out:

    Code:
    char * get(char * buffer, unsigned max, FILE * stream)
    {
     char * crlf = 0, * line = fgets(buffer, max, stream);
     if(line) crlf = strstr(line, "\n");
     if(crlf) *crlf = 0;
     return line; 
    }

    Also, look at this:

    >> char *scenarioNum;
    >> gets(scenarioNum);

    'scenarioNum' doesn't point to any memory!

    Don't use gets() either, since it doesn't provide buffer-overflow protection.

    Finally, look at the code that copies a file - wouldn't that make a great 'reusable' function? [hint hint]
    Code:
    #include <cmath>
    #include <complex>
    bool euler_flip(bool value)
    {
        return std::pow
        (
            std::complex<float>(std::exp(1.0)), 
            std::complex<float>(0, 1) 
            * std::complex<float>(std::atan(1.0)
            *(1 << (value + 2)))
        ).real() < 0;
    }

  8. #8
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    Thank you all. Your suggestions worked! I needed to strip the \n off of the end of the string (thanks for the code for that too).

  9. #9
    Been here, done that.
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    Originally posted by Sebastiani fgets() retrieves and stores the newline in the buffer - you have to strip it out:

    Code:
    char * get(char * buffer, unsigned max, FILE * stream)
    {
     char * crlf = 0, * line = fgets(buffer, max, stream);
     if(line) crlf = strstr(line, "\n");
     if(crlf) *crlf = 0;
     return line; 
    }
    How about:
    Code:
    char * get(char * buffer, unsigned max, FILE * stream)
    {
        int i;
        line = fgets(buffer, max, stream);
        i = strlen(line) - 1;
        if(line[i] == '\n') line[i] = '\0';
        return line; 
    }
    This saves the character by character search the strstr() uses. And if there is a return, it must be at the end of the string.

    But then when you think about it, what does strlen() do? Hmmm....

    But I have only one if. That must count for sumtin'
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  10. #10
    Guest Sebastiani's Avatar
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    The extra 'if' is necessary because fgets() might return NULL, in which case you wouldn't want to pass the pointer to a string-handling function anyway.
    Code:
    #include <cmath>
    #include <complex>
    bool euler_flip(bool value)
    {
        return std::pow
        (
            std::complex<float>(std::exp(1.0)), 
            std::complex<float>(0, 1) 
            * std::complex<float>(std::atan(1.0)
            *(1 << (value + 2)))
        ).real() < 0;
    }

  11. #11
    Been here, done that.
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    Originally posted by Sebastiani
    The extra 'if' is necessary because fgets() might return NULL, in which case you wouldn't want to pass the pointer to a string-handling function anyway.
    Good point...
    Definition: Politics -- Latin, from
    poly meaning many and
    tics meaning blood sucking parasites
    -- Tom Smothers

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