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Variable Length Arrays in C and C++
Here we will discuss about the variable length arrays in C++. Using this we can allocate an auto array of variable size. In C, it supports variable sized arrays from C99 standard. The following format supports this concept −
void make_arr(int n){
int array[n];
}
int main(){
make_arr(10);
}But, in C++ standard (till C++11) there was no concept of variable length array. According to the C++11 standard, array size is mentioned as a constant-expression. So, the above block of code may not be a valid C++11 or below. In C++14 mentions array size as a simple expression (not constant-expression).
Example
Let us see the following implementation to get better understanding −
#include<iostream>
#include<cstring>
#include<cstdlib>
using namespace std;
class employee {
public:
int id;
int name_length;
int struct_size;
char emp_name[0];
};
employee *make_emp(struct employee *e, int id, char arr[]) {
e = new employee();
e->id = id;
e->name_length = strlen(arr);
strcpy(e->emp_name, arr);
e->struct_size=( sizeof(*e) + sizeof(char)*strlen(e->emp_name) );
return e;
}
void disp_emp(struct employee *e) {
cout << "Emp Id:" << e->id << endl;
cout << "Emp Name:" << e->emp_name << endl;
cout << "Name Length:" << e->name_length << endl;
cout << "Allocated:" << e->struct_size << endl;
cout <<"---------------------------------------" << endl;
}
int main() {
employee *e1, *e2;
e1=make_emp(e1, 101, "Jayanta Das");
e2=make_emp(e2, 201, "Tushar Dey");
disp_emp(e1);
disp_emp(e2);
cout << "Size of student: " << sizeof(employee) << endl;
cout << "Size of student pointer: " << sizeof(e1);
}Output
Emp Id:101 Emp Name:Jayanta Das Name Length:11 Allocated:23 --------------------------------------- Emp Id:201 Emp Name:Tushar Dey Name Length:10 Allocated:22 --------------------------------------- Size of student: 12 Size of student pointer: 8
Updated on: 27-Aug-2020
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