- Data Structure
- Networking
- RDBMS
- Operating System
- Java
- MS Excel
- iOS
- HTML
- CSS
- Android
- Python
- C Programming
- C++
- C#
- MongoDB
- MySQL
- Javascript
- PHP
- Physics
- Chemistry
- Biology
- Mathematics
- English
- Economics
- Psychology
- Social Studies
- Fashion Studies
- Legal Studies
- Selected Reading
- UPSC IAS Exams Notes
- Developer's Best Practices
- Questions and Answers
- Effective Resume Writing
- HR Interview Questions
- Computer Glossary
- Who is Who
Why does C++ require a cast for malloc() but C doesn't?
In C language, the void pointers are converted implicitly to the object pointer type. The function malloc() returns void * in C89 standard. In earlier versions of C, malloc() returns char *. In C++ language, by default malloc() returns int value. So, the pointers are converted to object pointers using explicit casting.
The following is the syntax of allocating memory in C language.
pointer_name = malloc(size);
Here,
pointer_name − Any name given to the pointer.
size − Size of allocated memory in bytes.
The following is an example of malloc() in C language.
Example
#include <stdio.h> #include <stdlib.h> int main() { int n = 4, i, *p, s = 0; p = malloc(n * sizeof(int)); if(p == NULL) { printf("\nError! memory not allocated."); exit(0); } printf("\nEnter elements of array : "); for(i = 0; i < n; ++i) { scanf("%d", p + i); s += *(p + i); } printf("\nSum : %d", s); return 0; }
Output
Enter elements of array : 2 28 12 32 Sum : 74
In the above example in C language, if we do explicit casting, it will not show any error.
The following is the syntax of allocating memory in C++ language.
pointer_name = (cast-type*) malloc(size);
Here,
pointer_name − Any name given to the pointer.
cast-type − The datatype in which you want to cast the allocated memory by malloc().
size − Size of allocated memory in bytes.
The following is an example of malloc() in C++ language.
Example
#include <iostream> using namespace std; int main() { int n = 4, i, *p, s = 0; p = (int *)malloc(n * sizeof(int)); if(p == NULL) { cout << "\nError! memory not allocated."; exit(0); } cout << "\nEnter elements of array : "; for(i = 0; i < n; ++i) { cin >> (p + i); s += *(p + i); } cout << "\nSum : ", s; return 0; }
Output
Enter elements of array : 28 65 3 8 Sum : 104
In the above example in C++ language, if we will not do the explicit casting, the program will show the following error.
error: invalid conversion from ‘void*’ to ‘int*’ [-fpermissive] p = malloc(n * sizeof(int));