1 <!-- ##### SECTION Title ##### --> 2 Message Output and Debugging Functions 3 4 <!-- ##### SECTION Short_Description ##### --> 5 functions to output messages and help debug applications 6 7 <!-- ##### SECTION Long_Description ##### --> 8 <para> 9 These functions provide support for outputting messages. 10 </para> 11 <para> 12 The <function>g_return</function> family of macros (g_return_if_fail(), 13 g_return_val_if_fail(), g_return_if_reached(), g_return_val_if_reached()) 14 should only be used for programming errors, a typical use case is 15 checking for invalid parameters at the beginning of a public function. 16 They should not be used if you just mean "if (error) return", they 17 should only be used if you mean "if (bug in program) return". 18 The program behavior is generally considered undefined after one of these 19 checks fails. They are not intended for normal control flow, only to 20 give a perhaps-helpful warning before giving up. 21 </para> 22 23 <!-- ##### SECTION See_Also ##### --> 24 <para> 25 26 </para> 27 28 <!-- ##### SECTION Stability_Level ##### --> 29 30 31 <!-- ##### FUNCTION g_print ##### --> 32 <para> 33 Outputs a formatted message via the print handler. 34 The default print handler simply outputs the message to stdout. 35 </para> 36 <para> 37 g_print() should not be used from within libraries for debugging messages, 38 since it may be redirected by applications to special purpose message 39 windows or even files. 40 Instead, libraries should use g_log(), or the convenience functions 41 g_message(), g_warning() and g_error(). 42 </para> 43 44 @format: the message format. See the printf() documentation. 45 @Varargs: the parameters to insert into the format string. 46 47 48 <!-- ##### FUNCTION g_set_print_handler ##### --> 49 <para> 50 Sets the print handler. 51 Any messages passed to g_print() will be output via the new handler. 52 The default handler simply outputs the message to stdout. 53 By providing your own handler you can redirect the output, to a GTK+ 54 widget or a log file for example. 55 </para> 56 57 @func: the new print handler. 58 @Returns: the old print handler. 59 60 61 <!-- ##### USER_FUNCTION GPrintFunc ##### --> 62 <para> 63 Specifies the type of the print handler functions. 64 These are called with the complete formatted string to output. 65 </para> 66 67 @string: the message to be output. 68 69 70 <!-- ##### FUNCTION g_printerr ##### --> 71 <para> 72 Outputs a formatted message via the error message handler. 73 The default handler simply outputs the message to stderr. 74 </para> 75 <para> 76 g_printerr() should not be used from within libraries. Instead g_log() should 77 be used, or the convenience functions g_message(), g_warning() and g_error(). 78 </para> 79 80 @format: the message format. See the printf() documentation. 81 @Varargs: the parameters to insert into the format string. 82 83 84 <!-- ##### FUNCTION g_set_printerr_handler ##### --> 85 <para> 86 Sets the handler for printing error messages. 87 Any messages passed to g_printerr() will be output via the new handler. 88 The default handler simply outputs the message to stderr. 89 By providing your own handler you can redirect the output, to a GTK+ 90 widget or a log file for example. 91 </para> 92 93 @func: the new error message handler. 94 @Returns: the old error message handler. 95 96 97 <!-- ##### MACRO g_return_if_fail ##### --> 98 <para> 99 Returns from the current function if the expression is not true. 100 If the expression evaluates to %FALSE, a critical message is logged and 101 the function returns. This can only be used in functions which do not return 102 a value. 103 </para> 104 105 @expr: the expression to check. 106 107 108 <!-- ##### MACRO g_return_val_if_fail ##### --> 109 <para> 110 Returns from the current function, returning the value @val, if the expression 111 is not true. 112 If the expression evaluates to %FALSE, a critical message is logged and 113 @val is returned. 114 </para> 115 116 @expr: the expression to check. 117 @val: the value to return from the current function if the expression is not 118 true. 119 120 121 <!-- ##### MACRO g_return_if_reached ##### --> 122 <para> 123 Logs a critical message and returns from the current function. 124 This can only be used in functions which do not return a value. 125 </para> 126 127 128 129 <!-- ##### MACRO g_return_val_if_reached ##### --> 130 <para> 131 Logs a critical message and returns @val. 132 </para> 133 134 @val: the value to return from the current function. 135 136 137 <!-- ##### MACRO g_warn_if_fail ##### --> 138 <para> 139 Logs a warning if the expression is not true. 140 </para> 141 142 @expr: the expression to check 143 @Since: 2.16 144 145 146 <!-- ##### MACRO g_warn_if_reached ##### --> 147 <para> 148 Logs a critical warning. 149 </para> 150 151 @Since: 2.16 152 153 154 <!-- ##### FUNCTION g_on_error_query ##### --> 155 <para> 156 Prompts the user with <computeroutput>[E]xit, [H]alt, show [S]tack trace or [P]roceed</computeroutput>. 157 This function is intended to be used for debugging use only. The following 158 example shows how it can be used together with the g_log() functions. 159 </para> 160 <informalexample><programlisting> 161 #include <glib.h> 162 163 static void 164 log_handler (const gchar *log_domain, 165 GLogLevelFlags log_level, 166 const gchar *message, 167 gpointer user_data) 168 { 169 g_log_default_handler (log_domain, log_level, message, user_data); 170 171 g_on_error_query (MY_PROGRAM_NAME); 172 } 173 174 int main (int argc, char *argv[]) 175 { 176 g_log_set_handler (MY_LOG_DOMAIN, 177 G_LOG_LEVEL_WARNING | 178 G_LOG_LEVEL_ERROR | 179 G_LOG_LEVEL_CRITICAL, 180 log_handler, 181 NULL); 182 183 /* ... */ 184 </programlisting></informalexample> 185 <para> 186 If [E]xit is selected, the application terminates with a call to 187 <function>_exit(0)</function>. 188 </para> 189 <para> 190 If [H]alt is selected, the application enters an infinite loop. 191 The infinite loop can only be stopped by killing the application, 192 or by setting #glib_on_error_halt to %FALSE (possibly via a debugger). 193 </para> 194 <para> 195 If [S]tack trace is selected, g_on_error_stack_trace() is called. This 196 invokes <command>gdb</command>, which attaches to the current process and shows a stack trace. 197 The prompt is then shown again. 198 </para> 199 <para> 200 If [P]roceed is selected, the function returns. 201 </para> 202 <para> 203 This function may cause different actions on non-UNIX platforms. 204 </para> 205 206 @prg_name: the program name, needed by <command>gdb</command> for the [S]tack trace option. 207 If @prg_name is %NULL, g_get_prgname() is called to get the program name 208 (which will work correctly if gdk_init() or gtk_init() has been called). 209 210 211 <!-- ##### FUNCTION g_on_error_stack_trace ##### --> 212 <para> 213 Invokes <command>gdb</command>, which attaches to the current process and shows a stack trace. 214 Called by g_on_error_query() when the [S]tack trace option is selected. 215 </para> 216 <para> 217 This function may cause different actions on non-UNIX platforms. 218 </para> 219 220 @prg_name: the program name, needed by <command>gdb</command> for the [S]tack trace option. 221 If @prg_name is %NULL, g_get_prgname() is called to get the program name 222 (which will work correctly if gdk_init() or gtk_init() has been called). 223 224 225 <!-- ##### MACRO G_BREAKPOINT ##### --> 226 <para> 227 Inserts a breakpoint instruction into the code. On x86 and alpha systems 228 this is implemented as a soft interrupt and on other architectures it raises 229 a %SIGTRAP signal. 230 </para> 231 232 233 234
