I am trying out this code below.

#include<stdio.h>
#include<sys/types.h>
#include<sys/stat.h>
#include<fcntl.h>
int main()
{
    int fd;
    char filename[10];
    printf("enter the file name\n");
    scanf("%s",filename);
    fd=open(filename,O_RDONLY|O_CREAT|O_TRUNC,S_IRUSR);
    if(fd==-1)
    {
        printf("error opening file\n");
    }
    else
    {
        printf("file opened successfully\n");
    }
    return 0;
}

Here,I am settings file's permission such that only user can read this. When i execute this code for the first time it works as expected.But for the second time it shows the error message.My doubt is that why it is giving error message as I have already set the required permission mode in sync with flag modes.