Which of the following is the correct way to allocate a memory for the...
The sizeof operator returns the size of the struct in bytes. The size of a struct is not always the sum of the size of the individual members, hence use sizeof rather than a literal.
struct Student *sptr;
sptr = (struct Student*)malloc( sizeof(struct Student) );
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Which of the following is the correct way to allocate a memory for the...
Understanding Memory Allocation in C
When allocating memory for a structure in C, it's crucial to ensure that you are using the correct syntax and approach. Let's analyze option 'A' and why it is the correct choice.
Structure Definition
The structure is defined as follows:
c
struct Student {
int sid;
int age;
char grade;
};
This structure defines a `Student` with three members: an integer for student ID (`sid`), an integer for age (`age`), and a character for grade (`grade`).
Memory Allocation Using malloc
- Option A: Correct Usage
- `struct Student *sptr;`
- `sptr = (struct Student*)malloc(sizeof(struct Student));`
This option correctly:
- Declares a pointer `sptr` of type `struct Student*`.
- Allocates enough memory for a `Student` structure using `malloc`.
- Casts the returned pointer from `malloc` to `struct Student*`.
Why Other Options are Incorrect
- Option B: Incorrect Casting
- `sptr = (struct Student)malloc(sizeof(struct Student));`
Here, `malloc` returns a pointer, but it is incorrectly cast to a `struct Student`, which is not valid.
- Option C: Incorrect Dereferencing
- `sptr = (struct Student)*malloc(sizeof(struct Student));`
This option incorrectly attempts to dereference the pointer returned by `malloc`, which will lead to an error.
- Option D: Incorrect Size Calculation
- `sptr = (struct Student)malloc(sizeof(struct Student*));`
This option allocates memory for a pointer to `struct Student`, not for the structure itself, leading to insufficient memory allocation.
Conclusion
Option A is the correct way to allocate memory for the `Student` structure, adhering to proper syntax, memory allocation practices, and type casting. Always ensure that the size allocated matches the structure's size to avoid memory issues.
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