Can't create file with creat system call in c name taken from argument

Question

I am trying to create a file, the file name is will be taken from argument. Also the string that will be written is taken from argument! But the creat function returns -1. I could not find why? Any help appreciated!

C Code:

int main(int argc, char **argv)
{
    int fdc;
    int fdo;
    char *wr;
    char *rd;

    if (argc >= 3)
        wr = argv[2];
    else
        wr = "\0";
    printf("wr = %s\n", wr);
    if (argc >= 3)
    {
        fdc = creat(argv[1], O_RDWR);
        printf("fdc = %d\n", fdc);
        if (fdc != -1)
        {
            fdo = open(argv[1], O_RDWR);
            printf("fdo = %d", fdo);
            if (fdo != -1)
            {
                printf("a file created\n");
                write (fdo, wr, strlen(wr));
                printf("writed in file that created\n");
                read (fdo, rd, strlen(wr));
                printf("read done\n");
                printf("rd = %s\n",rd);
            }
            close(fdo);
        }
    }
}

Command:

get_next_line % ./a.out test.txt 012345

Output:

wr = 012345
fdc = -1

Answer 1

The second argument for creat function should be a mode, not a file flag.

S_IRWXU 00700 user (file owner) has read, write and execute permission
S_IRUSR 00400 user has read permission
S_IWUSR 00200 user has write permission
S_IXUSR 00100 user has execute permission
S_IRWXG 00070 group has read, write and execute permission
S_IRGRP 00040 group has read permission
S_IWGRP 00020 group has write permission
S_IXGRP 00010 group has execute permission
S_IRWXO 00007 others have read, write and execute permission
S_IROTH 00004 others have read permission
S_IWOTH 00002 others have write permission
S_IXOTH 00001 others have execute permission

from https://linux.die.net/man/2/open