Memory Management in C

This guide covers memory management in c with practical context and easy-to-follow details. Use it to understand the subject and apply the information confidently.

Void * calloc (int tongkichco, int kichco);

This function allocates an array of elements whose total size is tongkichco whose size of each element calculated in bytes will be kichco.

Void free (void * diachi);

This function frees a memory block defined by diachi.

Void * malloc (int tongkichco);

This function allocates dynamic memory with tongkichco size.

Void * realloc (void * diachi, int kichco_moi);

This function changes the size of allocated memory to a new size kichco_moi.

Allocate Dynamic Memory in C

When you program, you must be aware of the size of an array, then it is easy to define the array. For example, if you store a name of any person, it can be up to 100 characters so you can define the following:

 char ten_mang [100]; 

Now consider the case where you don't have an idea of the size of the array you intend to store, for example, you want to store a detailed description of a topic. Here you need to define a pointer to the character that does not define how much memory is required and then rely on the request we will allocate memory as the example below:

 #include #include #include int main () { char tennhanvien [ 100 ]; char * mieuta ; strcpy ( tennhanvien , "Tran Minh Chinh" ); /* Cap phat bo nho dong */ mieuta = ( char *) malloc ( 200 ); if ( mieuta == NULL ) { fprintf ( stderr , "Error - khong the cap phat bo nho theo yeu caun" ); } else { strcpy ( mieuta , "Chinh la nhan vien IT co nang luc chem gio tot!!!" ); } printf ( "Ten nhan vien la: %sn" , tennhanvien ); printf ( "Mieu ta: %sn" , mieuta ); printf ( "n===========================n" ); printf ( "QTM chuc cac ban hoc tot! n" ); } 

Compile and run the above C program to see the results:

The above program can be written using calloc (), instead of malloc as follows:

 mieuta = ( char *) calloc ( 200 , sizeof ( char )); 

So you have complete control of memory allocation and you can transmit any size value while allocating memory, unlike a fixed-length array that cannot be changed.

How to Change and Release Memory in C

Alternatively, you can increase or decrease the size of the allocated memory block by calling Realloc () . Please check the above program once and use the Realloc () And Free () functions :

 #include #include #include int main () { char tennhanvien [ 100 ]; char * mieuta ; strcpy ( tennhanvien , "Tran Minh Chinh" ); /* Cap phat bo nho dong */ mieuta = ( char *) malloc ( 100 ); if ( mieuta == NULL ) { fprintf ( stderr , "Error - khong the cap phat bo nho theo yeu caun" ); } else { strcpy ( mieuta , "Chinh la nhan vien IT co nang luc chem gio tot!!!" ); } /* Gia su ban muon luu tru mot mieuta nho hon */ mieuta = ( char *) calloc ( 50 , sizeof ( char )); if ( mieuta == NULL ) { fprintf ( stderr , "Error - khong the cap phat bo nho theo yeu caun" ); } else { strcat ( mieuta , "Anh ta rat gioi!!!" ); } printf ( "Ten nhan vien: %sn" , tennhanvien ); printf ( "Mieu ta: %sn" , mieuta ); /* giai phong bo nho voi ham free() */ free ( mieuta ); printf ( "n===========================n" ); printf ( "QTM chuc cac ban hoc tot! n" ); } 

Compile and run the above C program to see the results:

You can try the above example without using additional allocations and strcat () will report an error due to insufficient memory allocation.

According to Tutorialspoint

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