Differences

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--- programming:howtos-tips [2008/11/15 08:38]
cyril
+++ programming:howtos-tips [2014/04/16 18:07] (current)
cyril [Conversions with string]
@@ Line 1: / Line 1: @@
 ====== Howtos and Tips ======
+===== System =====
-===== Catching signals =====
+For details on functions search in the man page (''man <function-name>'' or ''man -a <function-name>'' if there is also a unix command with same name), or search the web.
+==== Catching signals ====
 => C and C++.
@@ Line 33: / Line 36: @@
 You can also change the signals actions with the [[http://www.opengroup.org/onlinepubs/007908799/xsh/sigaction.html|sigaction function]].
+==== Timer ====
+<code c>
+#include <unistd.h>
+unsigned int alarm(unsigned int seconds);
+</code>
+will trigger signal SIGALRM x seconds later that you can catch (see [[#catching_signals]]).
+If you need automatic repetition and/or sub-second precision, you can use:
+<code c>
+#include <sys/time.h>
+int setitimer(int whichtimer, const struct itimerval *value, struct itimerval *ovalue);
+</code>
+==== Waiting event ====
+Monitor multiple file descriptors.
+<code c>
+#include <sys/select.h>
+int select(int nfds, fd_set *readfds, fd_set *writefds,
+           fd_set *exceptfds, struct timeval *timeout);
+</code>
+==== Posix Threads ====
+<code c>
+#include <pthread.h>
+void *threadFunction(void *threadid)
+{
+	printf("%d: Hello World!\n", threadid);
+	pthread_exit(NULL);
+}
+int main (int argc, char *argv[])
+{
+	pthread_t threadId;
+	int threadData = 42;
+	if (pthread_create(&threadId, NULL, threadFunction, (void *)threadData) != 0)
+	{
+		printf("thread creation failed");
+		exit(1);
+	}
+	return 0;
+}
+</code>
+FIXME join sem etc
+==== Change program owner ====
+<code c>
+pwd = getpwnam("cyril");
+if (pwd)
+{
+	setgid(pwd->pw_gid);
+	setuid(pwd->pw_uid);
+}
+</code>
+But it doesn't really work to start shell commands, you should use ''sudo'' too:
+<code c>
+system("sudo -u cyril <command>);
+system("sudo -u cyril /bin/sh -c '<command1>; <command2>');
+</code>
 ===== Formatting IOs (iomanip) =====
@@ Line 48: / Line 117: @@
 <code cpp>
-std::cout << "normal text, "  << "\033[1;28m"
+std::cout << "normal text, "  << "\033[1;33m"
-          << "colored text, " << "\033[1;33m"
+          << "colored text, " << "\033[1;00m"
           << "normal text" << std::endl;
 </code>
@@ Line 113: / Line 182: @@
 <code c>
   #define ERROR(msg, ...) fprintf("ERROR:%s:%d# ", __FILE__, __LINE__, ## __VA_ARGS__);
+</code>
+You can also use the ''PRETTY_FUNCTION'' but it is not standard:
+<code>
+  #define ERROR(msg, ...) fprintf("ERROR:%s:%d %s# ", __FILE__, __LINE__, __PRETTY_FUNCTION__, ## __VA_ARGS__);
 </code>
@@ Line 137: / Line 210: @@
 #include <stdio.h>
 char s[128];
-sprintf("%d", 565);
+sprintf(s, "%d", 565);
 </code>
@@ Line 146: / Line 219: @@
 #include <stdlib.h>
 int i = atoi("562");
-float f = atof("4.5");
+long l = atol("4500294");
-double l = atol("4.546643");
+double f = atof("4.546643");
 </code>
@@ Line 165: / Line 238: @@
 ===== Function pointers =====
 The full test program is available [[http://www.rez-metz.supelec.fr/wiki/lib/exe/fetch.php/users:cyril:programming:function_pointers.cpp.txt|here]]
@@ Line 251: / Line 325: @@
  public:
   ...
-  double() { return data / (double)(1<<8); }
+  operator double() { return data / (double)(1<<8); }
 };