qio (3) - Linux Manuals

qio: Quick I/O routines for reading files


qio - Quick I/O routines for reading files


    #include <inn/qio.h>

    QIOSTATE *QIOopen(const char *name);

    QIOSTATE *QIOfdopen(int> I<fd);

    void QIOclose(QIOSTATE *qp);

    char *QIOread(QIOSTATE *qp);

    int QIOfileno(QIOSTATE *qp);

    size_t QIOlength(QIOSTATE *qp);

    int QIOrewind(QIOSTATE *qp);

    off_t QIOtell(QIOSTATE *qp);

    bool QIOerror(QIOSTATE *qp);

    bool QIOtoolong(QIOSTATE *qp);


The routines described in this manual page are part of libinn(3). They are used to provide quick read access to files; the QIO routines use buffering adapted to the block size of the device, similar to stdio, but with a more convenient syntax for reading newline-terminated lines. QIO is short for ``Quick I/O'' (a bit of a misnomer, as QIO provides read-only access to files only).

The QIOSTATE structure returned by QIOopen and QIOfdopen is the analog to stdio's FILE structure and should be treated as a black box by all users of these routines. Only the above API should be used.

QIOopen opens the given file for reading. For regular files, if your system provides that information and the size is reasonable, QIO will use the block size of the underlying file system as its buffer size; otherwise, it will default to a buffer of 8 KB. Returns a pointer to use for subsequent calls, or NULL on error. QIOfdopen performs the same operation except on an already-open file descriptor (fd must designate a file open for reading).

QIOclose closes the open file and releases any resources used by the QIOSTATE structure. The QIOSTATE pointer should not be used again after it has been passed to this function.

QIOread reads the next newline-terminated line in the file and returns a pointer to it, with the trailing newline replaced by nul. The returned pointer is a pointer into a buffer in the QIOSTATE object and therefore will remain valid until QIOclose is called on that object. If EOF is reached, an error occurs, or if the line is longer than the buffer size, NULL is returned instead. To distinguish between the error cases, use QIOerror and QIOtoolong.

QIOfileno returns the descriptor of the open file.

QIOlength returns the length in bytes of the last line returned by QIOread. Its return value is only defined after a successful call to QIOread.

QIOrewind sets the read pointer back to the beginning of the file and reads the first block of the file in anticipation of future reads. It returns 0 if successful and -1 on error.

QIOtell returns the current value of the read pointer (the lseek(2) offset at which the next line will start).

QIOerror returns true if there was an error in the last call to QIOread, false otherwise. QIOtoolong returns true if there was an error and the error was that the line was too long. If QIOread returns NULL, these functions should be called to determine what happened. If QIOread returned NULL and QIOerror is false, EOF was reached. Note that if QIOtoolong returns true, the next call to QIOread will try to read the remainder of the line and will likely return a partial line; users of this library should in general treat long lines as fatal errors.


This block of code opens /etc/motd and reads it a line at a time, printing out each line preceded by its offset in the file.

    QIOSTATE *qp;
    off_t offset;
    char *p;

    qp = QIOopen("/etc/motd");
    if (qp == NULL) {
        perror("Open error");
    for (p = QIOread(qp); p != NULL; p = QIOread(qp))
        printf("%ld: %s\n", (unsigned long) QIOtell(qp), p);
    if (QIOerror(qp)) {
        perror("Read error");


Written by Rich $alz <rsalz [at] uunet.uu.net> for InterNetNews. Updated by Russ Allbery <eagle [at] eyrie.org>.

$Id: qio.pod 9768 2014-12-07 21:22:57Z iulius $