UNIX for Dummies Questions & Answers

How can I use malloc with copying/creating files?

Is this the correct way?

I'm a bit confused...

Code:

   int in_fd;
   int *out_fd;
   char buffer;



   in_fd = open(av[1], O_RDONLY);
   out_fd = malloc(strlen(av[1])+strlen(av[2])+2);
   sprintf"(buffer,%s/%s", av[2],av[1]);

Sorry, could you give explanation of what it is you are trying to do ?
Are you trying to code a program to copy one file to another ?
If so, then usually you probably wouldnt bother malloc'ing memory - you could simply use a buffer allocated on stack of a given size, eg "char buffer[BUFSIZ];" and then read into and write from that buffer multiple times until the whole file has been copied. Obviously that buffer could be malloc'ed, but most people dont bother as you then have to handle a NULL return from malloc, and error handling, etc.

I hope this helps...

malloc has nothing to do with files.

Pretty sure he's trying to allocate memory to hold a string, like so:

Code:

// Enough mem to hold both strings, and '/', and the NULL terminator
char *buffer=malloc(strlen(av[1]) + strlen(av[2]) + 2);
sprintf(buffer, "%s/%s", av[1], av[2]);

printf("buffer is %s\n", buffer);

...

// once you know for sure nothing will ever use buffer anymore
free(buffer);

Does malloc allocate space for output files? That's what I had in mind, I was trying to dynamically allocate space from a read input file. It seems that malloc would be used only to create pathnames????

malloc allocates memory. You can use it for whatever you want.

I don't understand what you mean by 'for output files'. Could you tell me what you're actually trying to do?

sorry, I think i'm getting things mixed up.

I understand what mallocs does now. Thank you!