CODEWITHSUNDEEP
clinuxcopysystem-calls
korppu73
korppu73

Reputation: 339

C file copying program does not work for directory (on linux)

The following is a program that copies the contents of a file (1st argument) to a new file (2nd argument).

I'm testing it on linux, so for instance, copying the contents of user's terminal onto new file also works:

./copy /dev/tty newFile

However, copying the contents of current directory does not work:

./copy . newFile

The latter does not cause an error when opening the 1st argument, but nothing is copied. I thought that the contents of the directory would be copied onto the new file?

EDIT : This happens because linux takes working directory by standard to be ~

copy.c program below:

#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <unistd.h>


int copy(int inFileDesc,int outFileDesc);

int main (int argc, char** argv)
{
    int inputfd;
    int outputfd;
    if (argc!=3)
    {
        printf("Wrong number of arguments\n");
        exit(1);
    }
    inputfd=open(argv[1],O_RDONLY);
    if(inputfd==-1)
    {
        printf("Cannot open file\n");
        exit(1);
    }
    outputfd=creat(argv[2],0666);
    if(outputfd==-1)
    {
        printf("Cannot create file\n");
        exit(1);
    }
    copy(inputfd,outputfd);
    exit(0);
}

int copy(int inFileDesc,int outFileDesc)
{
    int count;
    char buffer[BUFSIZ];
    while((count=read(inFileDesc,buffer,sizeof(buffer)))>0)
    {
        write(outFileDesc,buffer,count);
    }
}

Upvotes: 1

Views: 71

Answers (1)

alamit
alamit

Reputation: 392

If you read man 2 open an man 2 read

man 2 open

The named file is opened unless:
...
[EISDIR] The named file is a directory, and the arguments specify that it is to
be opened for writing.

man 2 read

The pread(), read(), and readv() calls will succeed unless:
...
[EISDIR] An attempt is made to read a directory.

Therefore, open will not fail because you specified O_RDONLY and return your file descriptor, however read will fail at first call.

Upvotes: 2

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