CODEWITHSUNDEEP
csystem-callsfcntl
johnxx987
johnxx987

Reputation: 1

How can I unlock file in c

I tried to lock-unlock file in c. If the file is exist then there is no problem but if file does not exist and file is created, file stays locked. If I tried to open the file, It did not open. It says "there is no permission to open". Let's say file is: hey.txt, If it is exist there is no problem I can open this. But if hey.txt is not exist, file will created and write is done succesfully but I cannot open the file. I can only see file content when I wrote this sudo cat hey.txt to terminal

  #define WRITE_FLAGS (O_WRONLY  | O_CREAT | O_APPEND) //Write flag
        int main(int argc , char* argv[]){
       
    
        struct flock lock;
        int fd=open(argv[0],WRITE_FLAGS);
         int result_of_fcntl=0;
        if(fd==-1){
                perror("The file cannot opened.\n");
                return-1;
            }
        
            memset(&lock,0,sizeof(lock));
            lock.l_type=F_WRLCK;  
            result_of_fcntl=fcntl(fd,F_SETLKW,&lock);
        char buffer2[]={"deneme\n"};
        
                         
            int byteswritten = write(fd,buffer2,7);
            if(byteswritten==-1){
                perror("Error while writing to file:");
                return -1;
            }
        //unlock
            lock.l_type=F_UNLCK;
            result_of_fcntl=fcntl(fd,F_SETLKW,&lock);
            if(result_of_fcntl==-1){
                perror("Error:");
                return -1;
            }
            int closeFlag= close(fd);
            if(closeFlag==-1){
                perror("The file cannot closed.\n");
                return-1;
            }
         return 0;
}

Upvotes: 0

Views: 590

Answers (1)

datenwolf
datenwolf

Reputation: 162164

Your problem is not file locking, but improperly set file permission bits at reation time. Change your call to open like this:

open(filename, O_CREAT, S_IRUSR|S_IWUSR|S_IRGRP|S_IROTH);

Upvotes: 5

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