memset: a practical usage #Gregory

  • memset is a low-level C function.
  • memset takes a void pointer.
  • Fast and simple way to zero out an array of struct, having primitive data members. No std::string please. No ptr please. Use sizeof to get the byte count.
  • Useful in low level wire coding
// illustrates packed and memset
#include <iostream>
using namespace std;

struct A{
  unsigned int i1; //4 bytes
  bool b; //1 byte
  char cstr[2];
  int* ptr; //8 bytes
} __attribute__((packed));
size_t const cnt = 3;
A arr[cnt];
int main(){
  cout<<sizeof(A)<<endl;
  size_t sz = sizeof(arr);
  cout<<sz<<endl;
  memset(arr, 0, sz);
  for(size_t i=0; i<cnt; ++i){
    A* tmp = &arr[i];
    cout<<"i1 = "<<tmp->i1<<"; b = "<<tmp->b<<" ; cstr[1] = "<<(int)tmp->cstr[1]<<" ptr = "<<tmp->ptr<<endl;
  }
}
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