Loading data into a dynamic array

This is a discussion on Loading data into a dynamic array within the C++ Programming forums, part of the General Programming Boards category; Hi! I am reading data from a text file into a dynamically constructed array, like this: Code: static const unsigned ...

  1. #1
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    Loading data into a dynamic array

    Hi!

    I am reading data from a text file into a dynamically constructed array, like this:

    Code:
    static const unsigned pN = 1 << 13;
    
    float *p = NULL;
    p = new float[ pN ];
    
    // DATA
    FILE *file;
    
    file = fopen( "dist.txt" , "r" );
    
    unsigned int i = 0;
    
    while( !feof(file) ) {
        fscanf( file, "%f", p[ i ] );
        i++;
    }
    
    fclose(file);
    This works fine for arrays of float but does not work when I change the type to double? Any idea why, and how to fix it?

    Thanks for you help!
    Serge
    Last edited by serge; 06-18-2009 at 02:44 PM.

  2. #2
    Kernel hacker
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    Are you also changing %f to %lf to indicate that you mean double?

    --
    Mats
    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

  3. #3
    Captain Crash brewbuck's Avatar
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    Quote Originally Posted by serge View Post
    This works fine
    No, it doesn't work at all.
    Code:
    //try
    //{
    	if (a) do { f( b); } while(1);
    	else   do { f(!b); } while(1);
    //}

  4. #4
    The larch
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    Code:
    float arrp[ pN ];
    What's the purpose of this line? With doubles it takes twice the amount of stack memory and it is obviously two much - the stack is just a few megabytes for your program.

    BTW, in C++ you'd use std::vector to avoiding a) overallocating way too much, b) still running out of bounds in the file has more data than that.
    I might be wrong.

    Thank you, anon. You sure know how to recognize different types of trees from quite a long way away.
    Quoted more than 1000 times (I hope).

  5. #5
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    Quote Originally Posted by matsp View Post
    Are you also changing %f to %lf to indicate that you mean double?

    --
    Mats
    Thanks! This fixed the problem in fscanf.

    BTW: What is the difference between %f and %lf in printf?

  6. #6
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    Quote Originally Posted by anon View Post
    Code:
    float arrp[ pN ];
    What's the purpose of this line? With doubles it takes twice the amount of stack memory and it is obviously two much - the stack is just a few megabytes for your program.

    BTW, in C++ you'd use std::vector to avoiding a) overallocating way too much, b) still running out of bounds in the file has more data than that.
    Sorry for the confusion, this line was superflous, just deleted it in edit

  7. #7
    Captain Crash brewbuck's Avatar
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    Quote Originally Posted by serge View Post
    Thanks! This fixed the problem in fscanf.
    And yet the code you posted is still wrong. That isn't the real code, is it?
    Code:
    //try
    //{
    	if (a) do { f( b); } while(1);
    	else   do { f(!b); } while(1);
    //}

  8. #8
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    Quote Originally Posted by brewbuck View Post
    And yet the code you posted is still wrong. That isn't the real code, is it?
    ok, here is code that works
    Code:
    #include <iostream>
    
    int main()
    {
    static const unsigned N = 13;
    static const unsigned pN = 1 << N;
    
    double *p = NULL;
    p = new double[ pN ];
    
    unsigned int i;
    
    FILE *file;
    file = fopen( "dist.txt" , "r" );
    
    i = 0;
    
    while( !feof(file) ) {
        fscanf( file, "%lf", &p[ i ] );
        i++;
    }
    fclose(file);
    
    system( "PAUSE" );
    return 0;
    }

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  10. #10
    Captain Crash brewbuck's Avatar
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    Quote Originally Posted by serge View Post
    ok, here is code that works
    And the missing '&' appears!
    Code:
    //try
    //{
    	if (a) do { f( b); } while(1);
    	else   do { f(!b); } while(1);
    //}

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