[[programming:howtos-tips]]
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programming:howtos-tips [2008/11/15 08:29]
cyril 		programming:howtos-tips [2014/04/16 18:07] (current)
cyril [Conversions with string]
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 ====== Howtos and Tips ====== ====== 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++. => C and C++.
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 You can also change the signals actions with the [[http://www.opengroup.org/onlinepubs/007908799/xsh/sigaction.html|sigaction function]]. 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) ===== ===== Formatting IOs (iomanip) =====
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 for everything in this section. for everything in this section.
  
-==== Color ====+=== Color ===
  
  
 <code cpp> <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;           << "normal text" << std::endl;
 </code> </code>
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-==== Floating point precision ====+=== Floating point precision ===
  
 <code cpp> <code cpp>
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-==== Alignment ====+=== Alignment ===
  
  
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 </code> </code>
  
-==== White spaces ====+=== White spaces ===
  
 To get all characters while they are white spaces. To get all characters while they are white spaces.
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 <code c> <code c>
   #define ERROR(msg, ...) fprintf("ERROR:%s:%d# ", __FILE__, __LINE__, ## __VA_ARGS__);   #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> </code>
  
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 ===== Conversions with string ===== ===== Conversions with string =====
-==== From * to string ====+=== From * to string ===
 => C++ => C++
  
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 #include <stdio.h> #include <stdio.h>
 char s[128]; char s[128];
-sprintf("%d", 565);+sprintf(s, "%d", 565);
 </code> </code>
  
-==== From string to * ====+=== From string to * ===
 => C & C++ => C & C++
  
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 #include <stdlib.h> #include <stdlib.h>
 int i = atoi("562"); int i = atoi("562");
-float f = atof("4.5"); +long l = atol("4500294"); 
-double l = atol("4.546643");+double f = atof("4.546643");
 </code> </code>
  
  
-===== Define in makefile =====+===== #define in compiler command =====
  
 You can define names for the preprocessor from the command line (or the makefile) instead of the source file (''#define name''). It can be very useful. You can define names for the preprocessor from the command line (or the makefile) instead of the source file (''#define name''). It can be very useful.
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 ===== Function pointers ===== ===== 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]] 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]]
  
  
-==== Normal fn ====+=== Normal fn ===
  
 <code cpp> <code cpp>
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 </code> </code>
  
-==== Static member fn ====+=== Static member fn ===
  
 Static member functions behave the same way than normal functions. Static member functions behave the same way than normal functions.
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 </code> </code>
  
-==== Non virtual member fn ====+=== Non virtual member fn ===
  
 Member functions have a hidden parameter (a pointer to ''this''), so the pointer needs an object to call the function. If the member function is non virtual, the address of the member function is the same for all objects. Member functions have a hidden parameter (a pointer to ''this''), so the pointer needs an object to call the function. If the member function is non virtual, the address of the member function is the same for all objects.
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 </code> </code>
  
-==== Virtual member fn ====+=== Virtual member fn ===
  
 The syntax is the same as for non virtual member functions, and the pointer points to the place in the object where the address of the function is stored, so that it always points to the right function. The syntax is the same as for non virtual member functions, and the pointer points to the place in the object where the address of the function is stored, so that it always points to the right function.
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 ===== Cast overloading ===== ===== Cast overloading =====
-==== Cast from ====+=== Cast from ===
  
 This is done with constructors : This is done with constructors :
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 </code> </code>
  
-==== Cast to ====+=== Cast to ===
  
 The syntax is simple : The syntax is simple :
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  public:  public:
   ...   ...
-  double() { return data / (double)(1<<8); }+  operator double() { return data / (double)(1<<8); }
 }; };
  
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 </code> </code>
  
-==== Template cast ====+=== Template cast ===
  
 Imagine the following situation : Imagine the following situation :
programming/howtos-tips.1226737782.txt.gz · Last modified: 2013/09/19 16:43 (external edit)
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