# Linux Basic Programming -3

### Systems Calls for I/O Operations:-       

1. **Creat**:-      
`int creat(char *filename, mode_t mode);`   
First parameter is filename and second is mode.   Some most common modes are
    
**O_RDONLY**:- the file has read-only permission.  

**O_WRONLY**:- This mode gives write permissions.   

**O_RDWR**:- This mode gives both read and write permissions.    

**O_EXCL**:- This flag mode prevents the creation of a file if it already
exists.   

**O_APPEND**:- This mode appends the content to existing file data
without overriding it.    

**O_CREAT**:- This flag mode creates a file if it does not exist.       

If you want to use multiple modes at the same time, you can use the bitwise OR
operator.      

Program example:-  devnationfile_1.c        
 

```
#include<stdio.h>
#include<fcntl.h>

int main()
{
int file_descriptor;
char filename[255];
printf("Enter the filename:");
scanf("%s", filename);
//setting permission to read and write access for the file
file_descriptor = creat(filename, O_RDWR | O_CREAT);

if(file_descriptor!=-1){
 printf("file created successfully", filename);
 }
else{
 printf("unable to create the file");
 }
  return 0;
}```    

**Output**:-    

![devnationfile_1.png](https://cdn.hashnode.com/res/hashnode/image/upload/v1634255842992/7Udjak9VZ.png)
    
   2.**Open**:-      
`int open(const char *filepath, int flags, ...);`      
```    
#include<stdio.h>
#include<fcntl.h>
int main()
{
int file_descriptor;
char filename[255];
printf("Enter the filename:");
scanf("%s", filename);
 file_descriptor = open(filename, O_RDONLY);
if(file_descriptor!=-1){
 printf("%s file open successfully", filename);
 }
else{
 printf("unable to open the file%s ", filename);
 }  
  return 0;
}```    

3.**Close**:-    
`int close(int file_descriptor);`   
```   
int close_status = close(file_descriptor);
   // Checks the condition and prints the appropriate statement.
   /*
    Success: 0
    Error: -1
    */
   if(close_status == 0){
       printf("File Descriptor is closed Successfully\n");
   }else{
       printf("File Descriptor is not closed\n");
   }```
      

![devnationfile_opem_close.png](https://cdn.hashnode.com/res/hashnode/image/upload/v1634257253511/d3I04bIfV.png)
   
A file descriptor is an integer value that identifies the open file in a process.These are the most common operations that you can perform on files. All program uses core system calls to manipulate the tasks. To get more information on a system call, you can use the man command. For example, `man
creat` gives complete information on the creat system call.  These system calls set an error number if they fail to perform the operation.  


![man_creat.png](https://cdn.hashnode.com/res/hashnode/image/upload/v1634257687334/uFFyhwxQl.png)