sockets/rdwrn.c

This is sockets/rdwrn.c (Listing 61-1, page 1255), an example from the book, The Linux Programming Interface.

The source code file is copyright 2024, Michael Kerrisk, and is licensed under the GNU Lesser General Public License, version 3.

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Function list (Bold in this list means a function is not static)

#include <unistd.h>
#include <errno.h>
#include "rdwrn.h"                      /* Declares readn() and writen() */
ssize_t
readn(int fd, void *buffer, size_t n)
{
    ssize_t numRead;                    /* # of bytes fetched by last read() */
    size_t totRead;                     /* Total # of bytes read so far */
    char *buf;

    buf = buffer;                       /* No pointer arithmetic on "void *" */
    for (totRead = 0; totRead < n; ) {
        numRead = read(fd, buf, n - totRead);

        if (numRead == 0)               /* EOF */
            return totRead;             /* May be 0 if this is first read() */
        if (numRead == -1) {
            if (errno == EINTR)
                continue;               /* Interrupted --> restart read() */
            else
                return -1;              /* Some other error */
        }
        totRead += numRead;
        buf += numRead;
    }
    return totRead;                     /* Must be 'n' bytes if we get here */
}
ssize_t
writen(int fd, const void *buffer, size_t n)
{
    ssize_t numWritten;                 /* # of bytes written by last write() */
    size_t totWritten;                  /* Total # of bytes written so far */
    const char *buf;

    buf = buffer;                       /* No pointer arithmetic on "void *" */
    for (totWritten = 0; totWritten < n; ) {
        numWritten = write(fd, buf, n - totWritten);

        if (numWritten <= 0) {
            if (numWritten == -1 && errno == EINTR)
                continue;               /* Interrupted --> restart write() */
            else
                return -1;              /* Some other error */
        }
        totWritten += numWritten;
        buf += numWritten;
    }
    return totWritten;                  /* Must be 'n' bytes if we get here */
}

 

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