89 lines
3.1 KiB
Markdown
89 lines
3.1 KiB
Markdown
---
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title: Structures
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---
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## Structures in C
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### What are Structures?
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* A **structure** is a user-defined type in C. It is based on the idea that at certain times, a programmer wants to manage not just primitive data-types, but also programmer-defined data-types.
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* **Structure**, as the name suggests, consists of various primitive data-types, like character, integers, floating point variables, arrays, etc.
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* **Structure** can also contain various other user-defined data types. You would learn about nested-structures next.
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* **Structures** form the basis of **_object-oriented-programming_** as the concept of *class* originates from structures.
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### struct keyword
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* `struct` keyword can help us in defining a user-defined data type.
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```C
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struct StudentRecord
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{
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char Name[20];
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int Class;
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char Address[30];
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char Phone[10];
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};
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```
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* We can also define a **structure** using **typedef** which makes initializing a structure later in our program easier. Note that using typedef requires naming the structure, in the example below **struct StudentRecord** was given the name **Record**.
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```C
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typedef struct StudentRecord
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{
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char Name[20];
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int Class;
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char Address[30];
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char Phone[10];
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}Record;
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```
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In `main()`, the user-defined data-type **StudentRecord** is defined as:
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```C
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int main(void)
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{
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struct StudentRecord student1;
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}
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```
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the keyword struct must always precede **StudentRecord**, as it was not defined as a type.
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Using **typedef**, only the given name is sufficient to declare a type, so the user-defined data-type looks like:
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```C
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int main(void)
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{
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Record student1;
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}
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```
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To access the data stored in **student1**, we use dot( **.** ) operator to access the contents of the structure type variable.
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```C
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int main(void)
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{
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struct StudentRecord student1;
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student1.Class = 10;
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printf("Enter Name of Student\n");
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scanf("%s",&student1.Name);
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printf("Enter Address of Student\n");
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scanf("%s",&student1.Address);
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printf("Enter Phone Number of Student\n");
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scanf("%s",&student1.Phone);
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// Printing the Data
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printf("Name: %s \n, Class: %d \n, Address: %s \n, Phone: %s \n",student1.Name, student1.Class, student1.Address, student1.Phone);
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}
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```
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We can also dynamically allocate memory for a struct, as follows:
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```C
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Record *student1Ptr = (Record *)malloc(sizeof(Record));
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//always check for null after malloc
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```
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This will make malloc calculate the size of all the elements in the struct and allocate the appropriate amount of memory accordingly. To access members of a struct's pointer we use an arrow `->`
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```C
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int main(void)
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{
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Record *student1Ptr = (Record *)malloc(sizeof(Record));
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//check for null
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student1Ptr->Class = 10;
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printf("Enter Name of Student\n");
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scanf("%s",student1Ptr->Name);
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printf("Enter Address of Student\n");
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scanf("%s",student1Ptr->Address);
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printf("Enter Phone Number of Student\n");
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scanf("%s",student1Ptr->Phone);
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// Printing the Data
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printf("Name: %s \n, Class: %d \n, Address: %s \n, Phone: %s \n",student1->Name, student1->Class, student1->Address, student1->Phone);
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free(student1Ptr);
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}
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```
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### More Information
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https://www.tutorialspoint.com/cprogramming/c_structures.htm
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