VOLSTREAM_OPEN(3)

NAME
volstream_open - create a FILE* stream as a volatile stream buffer

SYNOPSIS
#include <volatilestream.h>

FILE *volstream_open(void);

struct volstream;

FILE *volstream_openv(struct volstream **vols);

int volstream_trunc(struct volstream *vols, size_tlength);

void *volstream_getbuf(struct volstream *vols);

size_t volstream_getsize(struct volstream *vols);

DESCRIPTION
A volatile stream is a stdio FILE* stream as a temporary dynamically allocated (and deallocated) memory buffer.

The volstream_open function opens a stdio stream as a temporary memory buffer. The buffer is dynamically allocated, grows as needed and it is automatically deallocated when the stream is closed.

The function volstream_openv has the same effect of volstream_open but it stores in vols a pointer that can be later used for volstream_trunc, volstream_getbuf and volstream_getsize.

volstream_trunc truncates the buffer to the requested length. If the current size of the buffer is larger than length the extra data is lost. If the buffer is shorter it is extended and the extended part is filled with null bytes.

volstream_getbuf and volstream_getsize return the current address and size of the buffer, respectively. These values remain valid only as long as the caller performs no further output on the stream or the stream is closed.

fflush is required before volstream_trunc, volstream_getbuf and volstream_getsize to flush the stream buffers.

RETURN VALUE
Upon successful completion volstream_open and volstream_open return a FILE pointer. Otherwise, NULL is returned and errno is set to indicate the error.

volstream_trunc returns -1 in case of error, 0 otherwise.

volstream_getbuf and volstream_getsize return the current address and size of the buffer, respectively.

EXAMPLES
The following example writes all the command arguments in a volatile stream, then it rereads the volatile stream one byte at a time:

    #include <stdio.h>
    #include <volatilestream.h>
    int main(int argc, char *argv[]) {
      FILE *f = volstream_open();
      int c;
      for (argv++; *argv; argv++)
        fprintf(f, "%s\n", *argv);
      fseek(f, 0, SEEK_SET);
      while ((c = getc(f)) != EOF)
        putchar(c);
      fclose(f);
    }

The following example has the same effect but it rereads the arguments as a memory buffer.

    #include <stdio.h>
    #include <unistd.h>
    #include <volatilestream.h>
    int main(int argc, char *argv[]) {
      struct volstream *vols;
      FILE *f = volstream_openv(&vols);
      int c;
      for (argv++; *argv; argv++) {
        fprintf(f, "%s\n", *argv);
      }
      fflush(f);
      ssize_t s = volstream_getsize(vols);
      char *buf = volstream_getbuf(vols);
    	write(STDOUT_FILENO, buf, s);
    	fclose(f);
    }

AUTHOR
VirtualSquare. Project leader: Renzo Davoli.