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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"><HTML><HEAD> <META NAME="GENERATOR" CONTENT="SGML-Tools 1.0.9"> <TITLE>GTK v1.2 Tutorial: glib</TITLE> <LINK HREF="gtk_tut-21.html" REL=next> <LINK HREF="gtk_tut-19.html" REL=previous> <LINK HREF="gtk_tut.html#toc20" REL=contents></HEAD><BODY BGCOLOR="#FFFFFF"><A HREF="gtk_tut-21.html">Next</A><A HREF="gtk_tut-19.html">Previous</A><A HREF="gtk_tut.html#toc20">Contents</A><HR NOSHADE><H2><A NAME="sec_glib"></A> <A NAME="s20">20. glib</A></H2><P>glib is a lower-level library that provides many useful definitionsand functions available for use when creating GDK and GTKapplications. These include definitions for basic types and theirlimits, standard macros, type conversions, byte order, memoryallocation, warnings and assertions, message logging, timers, stringutilities, hook functions, a lexical scanner, dynamic loading ofmodules, and automatic string completion. A number of data structures(and their related operations) are also defined, including memorychunks, doubly-linked lists, singly-linked lists, hash tables, strings(which can grow dynamically), string chunks (groups of strings),arrays (which can grow in size as elements are added), balanced binarytrees, N-ary trees, quarks (a two-way association of a string and aunique integer identifier), keyed data lists (lists of data elementsaccessible by a string or integer id), relations and tuples (tables ofdata which can be indexed on any number of fields), and caches.<P>A summary of some of glib's capabilities follows; not every function,data structure, or operation is covered here. For more completeinformation about the glib routines, see the glib documentation. Onesource of glib documentation is http://www.gtk.org/ <A HREF="http://www.gtk.org/">http://www.gtk.org/</A>.<P>If you are using a language other than C, you should consult yourlanguage's binding documentation. In some cases your language mayhave equivalent functionality built-in, while in other cases it maynot.<P><H2><A NAME="ss20.1">20.1 Definitions</A></H2><P>Definitions for the extremes of many of the standard types are:<P><BLOCKQUOTE><CODE><PRE>G_MINFLOATG_MAXFLOATG_MINDOUBLEG_MAXDOUBLEG_MINSHORTG_MAXSHORTG_MININTG_MAXINTG_MINLONGG_MAXLONG</PRE></CODE></BLOCKQUOTE><P>Also, the following typedefs. The ones left unspecified are dynamically setdepending on the architecture. Remember to avoid counting on the size of apointer if you want to be portable! E.g., a pointer on an Alpha is 8bytes, but 4 on Intel 80x86 family CPUs.<P><BLOCKQUOTE><CODE><PRE>char gchar;short gshort;long glong;int gint;char gboolean;unsigned char guchar;unsigned short gushort;unsigned long gulong;unsigned int guint;float gfloat;double gdouble;long double gldouble;void* gpointer;gint8guint8gint16guint16gint32guint32</PRE></CODE></BLOCKQUOTE><P><H2><A NAME="ss20.2">20.2 Doubly Linked Lists</A></H2><P>The following functions are used to create, manage, and destroystandard doubly linked lists. Each element in the list contains apiece of data, together with pointers which link to the previous andnext elements in the list. This enables easy movement in eitherdirection through the list. The data item is of type "gpointer",which means the data can be a pointer to your real data or (throughcasting) a numeric value (but do not assume that int and gpointer havethe same size!). These routines internally allocate list elements inblocks, which is more efficient than allocating elements individually.<P>There is no function to specifically create a list. Instead, simplycreate a variable of type GList* and set its value to NULL; NULL isconsidered to be the empty list.<P>To add elements to a list, use the g_list_append(), g_list_prepend(),g_list_insert(), or g_list_insert_sorted() routines. In all casesthey accept a pointer to the beginning of the list, and return the(possibly changed) pointer to the beginning of the list. Thus, forall of the operations that add or remove elements, be sure to save thereturned value!<P><BLOCKQUOTE><CODE><PRE>GList *g_list_append( GList *list, gpointer data );</PRE></CODE></BLOCKQUOTE><P>This adds a new element (with value <CODE>data</CODE>) onto the end of thelist.<P><BLOCKQUOTE><CODE><PRE> GList *g_list_prepend( GList *list, gpointer data );</PRE></CODE></BLOCKQUOTE><P>This adds a new element (with value <CODE>data</CODE>) to the beginning of thelist.<P><BLOCKQUOTE><CODE><PRE> GList *g_list_insert( GList *list, gpointer data, gint position );</PRE></CODE></BLOCKQUOTE><P>This inserts a new element (with value data) into the list at thegiven position. If position is 0, this is just like g_list_prepend();if position is less than 0, this is just like g_list_append().<P><BLOCKQUOTE><CODE><PRE>GList *g_list_remove( GList *list, gpointer data );</PRE></CODE></BLOCKQUOTE><P>This removes the element in the list with the value <CODE>data</CODE>;if the element isn't there, the list is unchanged.<P><BLOCKQUOTE><CODE><PRE>void g_list_free( GList *list );</PRE></CODE></BLOCKQUOTE><P>This frees all of the memory used by a GList. If the list elementsrefer to dynamically-allocated memory, then they should be freedfirst.<P>There are many other glib functions that support doubly linked lists;see the glib documentation for more information. Here are a few ofthe more useful functions' signatures:<P><BLOCKQUOTE><CODE><PRE> GList *g_list_remove_link( GList *list, GList *link );GList *g_list_reverse( GList *list );GList *g_list_nth( GList *list, gint n ); GList *g_list_find( GList *list, gpointer data );GList *g_list_last( GList *list );GList *g_list_first( GList *list );gint g_list_length( GList *list );void g_list_foreach( GList *list, GFunc func, gpointer user_data );</PRE></CODE></BLOCKQUOTE> <P><H2><A NAME="ss20.3">20.3 Singly Linked Lists</A></H2><P>Many of the above functions for singly linked lists are identical to theabove. Here is a list of some of their operations:<P><BLOCKQUOTE><CODE><PRE>GSList *g_slist_append( GSList *list, gpointer data ); GSList *g_slist_prepend( GSList *list, gpointer data ); GSList *g_slist_insert( GSList *list, gpointer data, gint position ); GSList *g_slist_remove( GSList *list, gpointer data ); GSList *g_slist_remove_link( GSList *list, GSList *link ); GSList *g_slist_reverse( GSList *list );GSList *g_slist_nth( GSList *list, gint n ); GSList *g_slist_find( GSList *list, gpointer data ); GSList *g_slist_last( GSList *list );gint g_slist_length( GSList *list );void g_slist_foreach( GSList *list, GFunc func, gpointer user_data ); </PRE></CODE></BLOCKQUOTE><P><H2><A NAME="ss20.4">20.4 Memory Management</A></H2><P><BLOCKQUOTE><CODE><PRE>gpointer g_malloc( gulong size );</PRE></CODE></BLOCKQUOTE><P>This is a replacement for malloc(). You do not need to check the returnvalue as it is done for you in this function. If the memory allocationfails for whatever reasons, your applications will be terminated.<P><BLOCKQUOTE><CODE><PRE>gpointer g_malloc0( gulong size );</PRE></CODE></BLOCKQUOTE><P>Same as above, but zeroes the memory before returning a pointer to it.<P><BLOCKQUOTE><CODE><PRE>gpointer g_realloc( gpointer mem, gulong size );</PRE></CODE></BLOCKQUOTE><P>Relocates "size" bytes of memory starting at "mem". Obviously, thememory should have been previously allocated.<P><BLOCKQUOTE><CODE><PRE>void g_free( gpointer mem );</PRE></CODE></BLOCKQUOTE><P>Frees memory. Easy one. If <CODE>mem</CODE> is NULL it simply returns.<P><BLOCKQUOTE><CODE><PRE>void g_mem_profile( void );</PRE></CODE></BLOCKQUOTE><P>Dumps a profile of used memory, but requires that you add #defineMEM_PROFILE to the top of glib/gmem.c and re-make and make install.<P><BLOCKQUOTE><CODE><PRE>void g_mem_check( gpointer mem );</PRE></CODE></BLOCKQUOTE><P>Checks that a memory location is valid. Requires you add #defineMEM_CHECK to the top of gmem.c and re-make and make install.<P><H2><A NAME="ss20.5">20.5 Timers</A></H2><P>Timer functions can be used to time operations (e.g. to see how muchtime has elapsed). First, you create a new timer with g_timer_new().You can then use g_timer_start() to start timing an operation,g_timer_stop() to stop timing an operation, and g_timer_elapsed() todetermine the elapsed time.<P><BLOCKQUOTE><CODE><PRE>GTimer *g_timer_new( void );void g_timer_destroy( GTimer *timer );void g_timer_start( GTimer *timer );void g_timer_stop( GTimer *timer );void g_timer_reset( GTimer *timer );gdouble g_timer_elapsed( GTimer *timer, gulong *microseconds );</PRE></CODE></BLOCKQUOTE> <P><H2><A NAME="ss20.6">20.6 String Handling</A></H2><P>glib defines a new type called a GString, which is similar to astandard C string but one that grows automatically. Its string datais null-terminated. What this gives you is protection from bufferoverflow programming errors within your program. This is a veryimportant feature, and hence I recommend that you make use ofGStrings. GString itself has a simple public definition:<P><BLOCKQUOTE><CODE><PRE>struct GString { gchar *str; /* Points to the string's current \0-terminated value. */ gint len; /* Current length */};</PRE></CODE></BLOCKQUOTE><P>As you might expect, there are a number of operations you can do witha GString.<P><BLOCKQUOTE><CODE><PRE>GString *g_string_new( gchar *init );</PRE></CODE></BLOCKQUOTE><P>This constructs a GString, copying the string value of <CODE>init</CODE>into the GString and returning a pointer to it. NULL may be given asthe argument for an initially empty GString.<P><BLOCKQUOTE><CODE><PRE>void g_string_free( GString *string, gint free_segment );</PRE></CODE></BLOCKQUOTE><P>This frees the memory for the given GString. If <CODE>free_segment</CODE> isTRUE, then this also frees its character data.<P><BLOCKQUOTE><CODE><PRE> GString *g_string_assign( GString *lval, const gchar *rval );</PRE></CODE></BLOCKQUOTE><P>This copies the characters from rval into lval, destroying theprevious contents of lval. Note that lval will be lengthened asnecessary to hold the string's contents, unlike the standard strcpy()function.<P>The rest of these functions should be relatively obvious (the _cversions accept a character instead of a string):<P><BLOCKQUOTE><CODE><PRE> GString *g_string_truncate( GString *string, gint len ); GString *g_string_append( GString *string, gchar *val ); GString *g_string_append_c( GString *string, gchar c ); GString *g_string_prepend( GString *string, gchar *val ); GString *g_string_prepend_c( GString *string, gchar c ); void g_string_sprintf( GString *string, gchar *fmt, ...); void g_string_sprintfa ( GString *string, gchar *fmt, ... );</PRE></CODE></BLOCKQUOTE> <P><H2><A NAME="ss20.7">20.7 Utility and Error Functions</A></H2><P><BLOCKQUOTE><CODE><PRE>gchar *g_strdup( const gchar *str );</PRE></CODE></BLOCKQUOTE><P>Replacement strdup function. Copies the original strings contents tonewly allocated memory, and returns a pointer to it.<P><BLOCKQUOTE><CODE><PRE>gchar *g_strerror( gint errnum );</PRE></CODE></BLOCKQUOTE><P>I recommend using this for all error messages. It's much nicer, and moreportable than perror() or others. The output is usually of the form:<P><BLOCKQUOTE><CODE><PRE>program name:function that failed:file or further description:strerror</PRE></CODE></BLOCKQUOTE><P>Here's an example of one such call used in our hello_world program:<P><BLOCKQUOTE><CODE><PRE>g_print("hello_world:open:%s:%s\n", filename, g_strerror(errno));</PRE></CODE></BLOCKQUOTE><P><BLOCKQUOTE><CODE><PRE>void g_error( gchar *format, ... );</PRE></CODE></BLOCKQUOTE><P>Prints an error message. The format is just like printf, but itprepends "** ERROR **: " to your message, and exits the program. Use only for fatal errors.<P><BLOCKQUOTE><CODE><PRE>void g_warning( gchar *format, ... );</PRE></CODE></BLOCKQUOTE><P>Same as above, but prepends "** WARNING **: ", and does not exit theprogram.<P><BLOCKQUOTE><CODE><PRE>void g_message( gchar *format, ... );</PRE></CODE></BLOCKQUOTE><P>Prints "message: " prepended to the string you pass in.<P><BLOCKQUOTE><CODE><PRE>void g_print( gchar *format, ... );</PRE></CODE></BLOCKQUOTE><P>Replacement for printf().<P>And our last function:<P><BLOCKQUOTE><CODE><PRE>gchar *g_strsignal( gint signum );</PRE></CODE></BLOCKQUOTE><P>Prints out the name of the Unix system signal given the signal number.Useful in generic signal handling functions.<P>All of the above are more or less just stolen from glib.h. If anyone caresto document any function, just send me an email!<P><HR NOSHADE><A HREF="gtk_tut-21.html">Next</A><A HREF="gtk_tut-19.html">Previous</A><A HREF="gtk_tut.html#toc20">Contents</A></BODY></HTML>⌨️ 快捷键说明
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