Previous: R Functions, Up: Reference
Below are the definitions for struct Rconn and struct fileconn copied from src/include/Rconnections.h. Additional comments by this author are inserted between special delimiters of the form /** comment **/.
struct Rconn { /** class name (null terminated) **/ char* class; /** description (null terminated), can be a filename, url, or other identifier, depending on the connection type **/ char* description; int enc; /* the encoding of 'description' */ /** file operation mode (null terminated) **/ char mode[5]; /** text - true if connection operates on text isopen - true if connection is open incomplete - used in @code{do_readLines}, @code{do_isincomplete}, and text_vfprintf, From `?connections`: true if last read was blocked, or for an output text connection whether there is unflushed output canread - true if connection is readable canwrite - true if connection is writable canseek - true if connection is seekable blocking - true if connection reads are blocking isGzcon - true if connection operates on gzip compressed data **/ Rboolean text, isopen, incomplete, canread, canwrite, canseek, blocking, isGzcon; /** function pointers for I/O operations **//** open - called when the connection should be opened args: struct Rconn * - an initialized connection to be opened return: Rboolean - true if connection successfully opened, false otherwise **/ Rboolean (*open)(struct Rconn *);/** close - called when the connection should be closed args: struct Rconn * - a connection to be closed **/ void (*close)(struct Rconn *); /* routine closing after auto open *//** destroy - called after the connection is closed in order to free memory, and other cleanup tasks args: struct Rconn * - a connection to be closed **/ void (*destroy)(struct Rconn *); /* when closing connection *//** vfprintf - variable argument list version of printf for a connection args: struct Rconn * - a connection where items should be printed const char * - a format string in the style of the printf family va_list - a variable argument list containing the items referred to in the format string return: int - number of characters printed, negative on failure **/ int (*vfprintf)(struct Rconn *, const char *, va_list);/** fgetc - get a (re-encoded) character from the connection args: struct Rconn * - a connection to be read return: int - a (re-encoded) character, or R_EOF **/ int (*fgetc)(struct Rconn *);/** fgetc_internal - get a character from the connection args: struct Rconn * - a connection to be read return: int - a character, or R_EOF **/ int (*fgetc_internal)(struct Rconn *);/** seek - seek to a new position in the connection args: struct Rconn * - a connection to seek double - offset to seek relative to origin, apparently double is used here to avoid using integer types, i.e. long int, which is the prototype of the corresponding parameter in fseek, as defined in stdio.h int - the origin of seeking, 1 (and any except 2 and 3) if relative to the beginning of the connection, 2 if relative to the current connection read/write position, 3 if relative to the end of the connection int - currently only used by file_seek to select the read or write position when the offset is NA return: double - the read/write position of the connection before seeking, negative on error double is again used to avoid integer types **/ double (*seek)(struct Rconn *, double, int, int);/** truncate - truncate the connection at the current read/write position. args: struct Rconn * - a connection to be truncated **/ void (*truncate)(struct Rconn *);/** fflush - called when the connection should flush internal read/write buffers args: struct Rconn * - a connection to be flushed return: int - zero on success, non-zero otherwise **/ int (*fflush)(struct Rconn *);/** read - read in the style of fread args: void * - buffer where data is read into size_t - size (in bytes) of each item to be read size_t - number of items to be read struct Rconn * - a connection to be read return: size_t - number of _items_ read **/ size_t (*read)(void *, size_t, size_t, struct Rconn *);/** write - write in the style of fwrite args: void * - buffer containing data to be written size_t - size (in bytes) of each item to be written size_t - number of items to be written struct Rconn * - a connection to be written return: size_t - number of _items_ written **/ size_t (*write)(const void *, size_t, size_t, struct Rconn *); /** cached and pushBack data nPushBack - number of lines of cached/pushBack storage posPushBack - read position on current line of storage PushBack - cached/pushBack data lines ('\n' delimited) save - used to store the character following a \n, if not \r save2 - used to store a character from Rconn_ungetc **/ int nPushBack, posPushBack; /* number of lines, position on top line */ char **PushBack; int save, save2; /** character re-encoding with iconv encname - character encoding string (null terminated), this string must be one of the standard encoding strings used by [lib]iconv inconv - input character encoding context (iconv_t) outconv - output character encoding context (iconv_t) iconvbuff - input character encoding buffer oconvbuff - output character encoding buffer next - only used by dummy_fgetc, points to the next re-encoded character for reading init_out - storage for output iconv initialization sequence navail - iconv buffer offset inavail - iconv buffer offset EOF_signalled - true if EOF reached UTF8out - true if connection writes UTF8 encoded characters **/ char encname[101]; /* will be iconv_t, which is a pointer. NULL if not in use */ void *inconv, *outconv; /* The idea here is that no MBCS char will ever not fit */ char iconvbuff[25], oconvbuff[50], *next, init_out[25]; short navail, inavail; Rboolean EOF_signalled; Rboolean UTF8out; /** finalization pointers id - unique id, used to "ensure that the finalizer does not try to close connection after it is alread closed" (quoted from source code), but also to identify the connection to be finalized. Using an arbitrary but unique id here is clever, it means the connections internals are further protected from passing references to connection structures. ex_ptr - external pointer, referenced by finalizer code **/ void *id; void *ex_ptr; /** private user data (i.e. FILE *, offsets etc.) **/ void *private; };
typedef struct fileconn {
/** stream pointer for file connection **/
FILE *fp;
/** read/write offsets **/
#if defined(HAVE_OFF_T) && defined(HAVE_FSEEKO)
off_t rpos, wpos;
#else
#ifdef Win32
off64_t rpos, wpos;
#else
long rpos, wpos;
#endif
#endif
/** last_was_write - true if last file operation was write **/
Rboolean last_was_write;
/** raw - true if a raw file connection **/
Rboolean raw;
#ifdef Win32
/** anon_file - true if file is temporary or 'anonymous' **/
Rboolean anon_file;
/** name - expanded filename of temporary file **/
char name[PATH_MAX+1];
#endif
} *Rfileconn;