[c/c++]_[Primary]_[programming error-prone place]

Scene:

1. Here is a summary of some of the daily error-prone details.

Issue 1: A Class A has a member variable int deleted, given an object pointer of a *a, to determine deleted is true when the output of a statement.

In general, the Novice will write this:

if (a) {if (a->deleted)       {           cout << "deleted" << Endl;       }}

But this is not enough to streamline and waste the number of lines, it should be.

if (a && a->deleted) {    cout << "deleted" << Endl;}

Issue 2: Create a path string for tchar* (wchar_t*).

Note: The size of malloc out is not the same as the size of the array declaration, do you think the following storage path is large enough?

wchar_t* info = (wchar_t*) malloc (MAX_PATH);

This defines the size of only Max_path bytes and cannot store max_path wide bytes. To define this to support MAX_PATH-size wide-byte, the following is the same:

#include <iostream> #include <stdlib.h>using namespace std;int main (int argc, char const *argv[]) {wchar_t* info = (wchar_t*) malloc (sizeof (wchar_t) *max_path) std::cout << "sizeof (wchar_t) *max_path:" << sizeof ( wchar_t) *max_path << std::endl;wchar_t info2[max_path];std::cout << "Info2:" << sizeof (Info2) < < Std::endl;return 0;}

Output:

sizeof (wchar_t) *max_path:520info2:520

Question 3: Mistakenly assume that pointer +1 is the address value +1

The rule for pointer p+n is (char*) p + sizeof (*P) *n, that is, the size of the P pointer type determines the increment in multiples.

#include <iostream> #include <stdlib.h>using namespace std;int main (int argc, char const *argv[]) {wchar_t* info = (wchar_t*) malloc (sizeof (wchar_t) *max_path) std::cout << "sizeof (wchar_t) *max_path:" << sizeof ( wchar_t) *max_path << std::endl;wchar_t info2[max_path];std::cout << "Info2:" << sizeof (Info2) < < Std::endl;std::cout << (int*) Info << ":" << (int*) (info+1) << Std::endl; Std::cout << (int*) ((char*) (info) +sizeof (*info) *) << ":" << (int*) (info+1) << Std::endl; return 0;}

Output:

sizeof (wchar_t) *MAX_PATH:520INFO2:5200X506CC0:0X506CC20X506CC2:0X506CC2

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[c/c++]_[Primary]_[programming error-prone place]