---
name: "volstream_open"
section: "3"
platform: "linux"
package: "libvolatilestream-dev"
version: "1.0.2-1+b1"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/volstream_open"
---

# volstream\_open(3)

create a FILE\* stream as a volatile stream buffer

## NAME

**volstream\_open** – create a FILE\* stream as a volatile stream buffer

## SYNOPSIS

**#include \<volatilestream.h\>**

**FILE \*volstream\_open(void);**

**int volstream\_trunc(FILE \****f***, size\_t** *length***);**

**int volstream\_getbuf(FILE \****f***, void \*\****buf***, size\_t \****buflen***);**

## 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.

**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** writes the current address and size of the buffer in **\*buf** and **\*buflen** respectively. These values remain valid only as long as the caller performs no further output on the stream or the stream is closed.

## RETURN VALUE

Upon successful completion **volstream\_open** returns a FILE pointer. Otherwise, NULL is returned and errno is set to indicate the error.

**volstream\_trunc** and **volstream\_getbuf** return 0 or -1 if an error occurred. In the event of an error, errno is set to indicate the error.

## 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[]) {
    FILE *f = volstream_open();
    int c;
    for (argv++; *argv; argv++) {
      fprintf(f, "%s\n", *argv);
    }
    fflush(f);
    ssize_t s;
    void *buf;
    volstream_getbuf(f, &buf, &s);
    write(STDOUT_FILENO, buf, s);
    fclose(f);
  }
  ```

## AUTHOR

VirtualSquare. Project leader: Renzo Davoli.