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How does the RAM work in C++ computing?

This is a discussion on How does the RAM work in C++ computing? within the C++ Programming forums, part of the General Programming Boards category; Hello all: In my knowledge that the usefulness of RAM in computing is for storing data such as array. That’s ...

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    How does the RAM work in C++ computing?

    Hello all:

    In my knowledge that the usefulness of RAM in computing is for storing data such as array. That’s why we need large RAM If the program is large. BUT recently I am confused.

    I have 2-PC, one old Toshiba Satellite and a new HP pavilion. Both re-installed with XP pro sp3. By “My Computer/ Properties /General” check them, the memory are: 1.00 GB of RAM and
    2.90 GB RAM.

    I have a stock program with large 2-dimension array, the 1st array for storing tickers and the 2nd for quotes. Because of large tickers and quotes, it’s sure that it requires large memory/RAM.

    Using VC++2008, II run this program in the old, RAM=1 GB, PC, it prompts the small grey/silver window, with ‘Debug’ ‘Send Error Report’ ‘Don’t Send’ three press button, meaning that RAM is not enough to store all the 2-dimension array/variables.

    I transferred to run it in the new, RAM=2.9 GB, PC. To my surprise the result is the same: appeared the gray/silver small window the same.

    I decrease the size of the 2-dimension variable/array, both PCs are OK.

    Repeated experiments showed: both PC have the same ability to store variable/array! CAN

    1.0 GB of RAM = 2.90 GB of RAM ???

    I am stunned! Could you helped me?

  2. #2
    and the Hat of Guessing tabstop's Avatar
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    Variables on the stack != RAM.

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    Captain Crash brewbuck's Avatar
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    I took a Honda Civic and a Chevy Suburban and threw them off a cliff. They both shattered into little pieces. Amazingly, a Honda Civic seems to be indistinguishable from a Chevy Suburban. I am stunned.
    Code:
    //try
    //{
    	if (a) do { f( b); } while(1);
    	else   do { f(!b); } while(1);
    //}

  4. #4
    spurious conceit MK27's Avatar
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    Quote Originally Posted by YuminZhao View Post
    I have a stock program with large 2-dimension array, the 1st array for storing tickers and the 2nd for quotes. Because of large tickers and quotes, it’s sure that it requires large memory/RAM.
    Is the array on the heap or in the stack? I'm not a VC++ or MS user, so I dunno about your error popup, but if the array is on the stack, the size of the stack is predetermined by the compiler, it will be the same regardless of the total RAM, and it will be much less than a GB.

    Quick google reveals Visual Studio 2005 has a default stack size of 1 MB.

    /F (Set Stack Size) (C++)
    C programming resources:
    GNU C Function and Macro Index -- glibc reference manual
    The C Book -- nice online learner guide
    Current ISO draft standard
    CCAN -- new CPAN like open source library repository
    3 (different) GNU debugger tutorials: #1 -- #2 -- #3
    cpwiki -- our wiki on sourceforge

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    and the hat of wrongness Salem's Avatar
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    I second tabstop.

    > I decrease the size of the 2-dimension variable/array, both PCs are OK.
    > Repeated experiments showed: both PC have the same ability to store variable/array!
    I'm guessing you reduced the size of your array down to something in the region of say 1MB.

    Regardless of how much physical RAM the machine has, windows gives each process a virtual 1MB of stack space. Almost all of the rest (up to about 1/2 the virtual address space (approx 2GB) you can allocate using new(C++) or malloc(C)

    But you need to post actual code to get a proper answer.
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