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POAccurately Calculating the Memory used by a C++ Programming
 

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  1. POAccurately Calculating the Memory used by a C++ Programming
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    <p>A program I am writing for work needs to keep track of the memory used by itself. But it can't monitor its memory usage as a whole, I need it to monitor each object in the program and how much memory that object is using, that way it can then tell that object to cut back on memory usage if it using above a certain capacity. The part that monitors memory usage holds a pointer to all created objects and keeps track of their memory usage by calling a method on that object that returns the size of the object.</p> <p>The problem I'm having is that I cannot accurately calculate the size of the memory used. It doesn't matter if my calculation are off by a little bit but I'm getting big difference. The size that my program calculates varies (depending on which actions the program performs) between 1/2 to 2/3 of the actual memory usage of the program. For example a program that used 3.35gb of ram was calculated to only be using 2.16gb.</p> <p>The current way I calculate the size of an object is by adding sizeof(*this) to the length of any vectors or arrays in the object multiplied by the sizeof the elements in the vector/array.</p> <p>Is there something wrong with the way I'm calculating the memory used? Or is there just something else I'm not taking into account? If anyone knows of a program that you can analyse memory usage by different aspects of a program that would also be very helpful, that way I can track down where all this extra memory is coming from (preferably one that can run on Linux without GUI as I'm using Ubuntu server, but also have a windows machine I can use).</p>
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    1. USDavid Saxon
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    1. COWhat objects do you keep in those vectors? If those objects allocate memory dynamically (using `new`, `malloc` and the like), `sizeof` won't account for the space consumed by this.
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      1. USjogojapan
    2. COThe problem probably comes from the program you are using to tell you how much memory has been allocated to your application (not your code doing the calculation). The problem is that this program is adding the sum of pages that have been assigned to your application by the OS. The runtime then does its own memory management using the pages allocated (not all the memory may be allocated to objects).
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      1. USMartin York
    3. COOne simple thing: if a lot of your memory is in vectors, remember to use their capacity and not their size to estimate actual memory "usage" (i.e. occupation of virtual addresses) as opposed to theoretical memory usage (memory actually useful employed). Other containers are much more expensive because of container overhead (usually several pointers per element, which adds up fast when the elements are small objects like integer.)
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