<<C++ Programming Excercises in CSAPP

programming › cs 61

Ps0

seems nice.

Sec 1

  1. can’t call ++it when it == container.end(), otherwise segmentation fault.

  2. Prefer ++i than i++

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    i = 1;
    j = ++i; //(i is 2, j is 2)
       
    i = 1;
    j = i++; // (i is 2, j is 1)

Ps1: a debugging memory allocator

Context:

  1. malloc is not perfect and can fail due to various reasons such as size was too big/memory is exhausted/…
  2. undefined behavior: any program that invokes undefined behavior has no meaning.

Syntax:

  1. const

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    // const pointer point to const member function which takes const pointer 
    // to a const int. The last const means this is a const member function
    // (can't modify variables of the this instance)
    const int* const myClassMethod(const int* const & param) const;

  2. type casting

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    // internal metadata
    std::unordered_map<uintptr_t, size_t> payload;
    payload.insert({(uintptr_t)ptr, sz});

Problem:

  1. How to count the allocations?
    • augmentation
  2. When will allocation fail?
    • Stuck for two hours. I thought I could not modify funcation signature(return type). Therefore I overlooked the right direction.
    • ?relation in heap max address and failed allocations. Answer: when malloc fails, base_alloc(malloc) will return a nullptr, which is the usual case.
  3. allocated address of heap: overlap with other regions
    • Key: heap_first
    • Answer: should set heap_min only once

Design:

  1. Basic version:
    • use hash table(pointer value/address: size)
    • bounded metadata: last N freed allocations, and set N = 10.
      • should check size once updates data
  2. augmentation: use a struct

Problem:

  1. where to put metadata?
    • global use
  2. How to bound metadata?
    • First, what is bounded metadata?
      • ex: a bounded amount of metadata about freed allocations, such as statistics or a list of the last N freed allocations.