https://robark.gitlab.io/pointers/index.htmlPointersHugoen-usFri, 10 May 2024 11:10:06 -0700https://robark.gitlab.io/pointers/intro/index.htmlThu, 03 Jun 2021 22:53:15 +0000https://robark.gitlab.io/pointers/intro/index.htmlPointers Intro #include <iostream> using namespace std; int main(){ /* //int* p,q,r; //q and r are not pointers int* p; int* q; int* r; int *p, *q, *r; //p, q and r are all pointers */ int a; int *iptr; a = 2; iptr = &a; cout<<a<<endl; //2 cout<<iptr<<endl; //address of iptr *iptr = 6; cout<<a<<endl; //6 return 0; } Passing by reference vs passing pointers (only C++ has pass by ref. Must use pointers in C)https://robark.gitlab.io/pointers/const_arith/index.htmlMon, 07 Jun 2021 22:41:59 +0000https://robark.gitlab.io/pointers/const_arith/index.htmlConstant Pointers and pointer arithmetic Constant pointers #include <iostream> using namespace std; int main(){ int a(5); int b(6); //const pointer const int *p; // *p=1 illegal but p=&a is legal // can't change value which p points to (p is a movable pointer but it's read only) p=&a; cout << *p << endl; p=&b; cout << *p << endl; //*p=7; //illegal //pointer const int* const q(&a); // q = &b illegal but *q=1 okay //must initialize q at creation. Can't change location where p points to a=9; cout << a <<endl; *q=8; //okay cout << a << " " <<*q <<endl; //q=&b; // illegal return (0); } //easy way to remember if const comes first it's a movable read only pointer // if it comes after int* then it's a fixed arrow but read/writeable. //const int* const xp(&a) is possible Pointer Arithmetichttps://robark.gitlab.io/pointers/new_delete/index.htmlTue, 08 Jun 2021 23:17:27 +0000https://robark.gitlab.io/pointers/new_delete/index.htmlDynamic memory allocation: new and delete #include <iostream> #include <stdio.h> #include <string.h> using namespace std; void leak(){ int* q=new int; *q=1; } int main(){ int* p; p = new int; //allocated on heap (only way possible to reference this newly allocated memory is //through the pointer p. Possible pitfall. Every new requires a corresponding delete *p=5; cout<<p<<endl; cout << *p <<endl; delete p; p=nullptr; // p=0; cout<<p<<endl; leak(); //memory leak function /* cout << *p <<endl; //read memory *p=4; //writing to memory cout << *p <<endl; */ return (0); } // all memory freed on stackhttps://robark.gitlab.io/pointers/arrays/index.htmlThu, 10 Jun 2021 23:13:23 +0000https://robark.gitlab.io/pointers/arrays/index.htmlPointer Arrays #include <iostream> #include <cstring> using namespace std; void mystrncpy(char* p, string s, unsigned int n){ unsigned int siz; if ( s.size() < n) siz= s.size(); else siz=n; unsigned int x; for (x=0; x<siz; x++) { //*(p+x)=s[x]; p[x]=s[x]; } p[x]='\0'; //null char terminated } int main(){ char* c; c= new char[5]; //mystrncpy(c,"abcde",4); strncpy(c,"abcdef",5-1); //strncpy(c,"abc",5-1); //in line above, can't use sizeof(c) as c is just a pointer cout <<"strlen(c): "<< strlen(c) <<endl; cout<<endl; printf("%s\n", c); cout << *c << endl; //first letter cout << c << endl; // cstring c delete[] c; return 0; } C code commentedhttps://robark.gitlab.io/pointers/void-func/index.htmlFri, 11 Jun 2021 23:24:58 +0000https://robark.gitlab.io/pointers/void-func/index.htmlC string arrays using pointers / struct pointers / void pointers / function pointers C string arrays using pointers and dynamic memory #include <stdio.h> #include <fstream> // ofstream ifstream #include <iostream> #include <cstring> //#include <algorithm> //count using namespace std; unsigned int filesize(const char* fname){ ifstream f(fname); string dummy; unsigned int lines=0; /* //------------------- while( getline(f, dummy) ) { lines++; } //------------------- */ char c; while ( !f.eof() ) { c = f.get(); if ( c == '\n' ) lines++; } //------------------- //count requires algorithm //lines= count(istreambuf_iterator<char>(f), istreambuf_iterator<char>(), '\n'); //------------------- f.close(); cout<<lines<< " lines in file "<<fname<<endl; return lines; } int main(){ string s; unsigned int c=0; const unsigned int lines = filesize("fruit.txt"); char** v; v = new char* [lines]; ifstream inf("fruit.txt"); while ( getline(inf,s) ) { v[c] = new char [s.size()+1]; // +1 for null byte .c_str() //strncpy(v[c], s.c_str(), s.size()+1); strcpy(v[c], s.c_str()); c++; } cout << "v = "<<v<<endl; //memory address cout << "v[0] = "<<v[0]<<endl; // first line cout << "v[0][0] = "<<v[0][0]<<endl; //first char of first line cout<<c<<endl; for (unsigned int x=0; x<c; x++) { printf("%s\n", v[x]); delete[] v[x]; v[x]=nullptr; } delete[] v; v=nullptr; return 0; } Struct pointers and arrow operatorhttps://robark.gitlab.io/pointers/decay/index.htmlFri, 10 May 2024 11:10:06 -0700https://robark.gitlab.io/pointers/decay/index.htmlPointer Decay Here is an example of an array decaying to a pointer when it is passed to a function #include <iostream> using namespace std; //example of array decaying to a pointer when passed to a function void init(int a[] ){ // array decays to a pointer cout << "In func init" <<endl; cout << sizeof(a) <<endl; //8 cout << sizeof(a[0]) <<endl; //4 size_t s= sizeof(a)/sizeof(a[0]); cout << s << endl; //2 // On 64 bit OS's // a pointer is 64 bits (8 bytes) and an int is 32 bits (4 bytes) //for (int x=0; x<s; x++) //cannot iterate over array since size is unknown } //proper way of passing a C array. We must also pass the size void propinit(int *a, size_t s ){ cout << "in func init2" <<endl; for (size_t x=0; x<s; x++) { a[x]=x; cout << a[x] ; } cout << endl; } int main(){ int a[6]; cout << sizeof(a) <<endl; //24 cout << sizeof(a[0]) <<endl; //4 size of int size_t s= sizeof(a)/sizeof(a[0]); // 24/4 cout << s << endl; //6 init(a); //pass array to function init propinit(a,6); //pass array and the size return 0; }