run Python script in Android.mk on Android building system Friday, September 23, 2011

Insert the bellowing line into Android.mk

$(shell python $(LOCAL_PATH)/scripts/myprepare.py)

When running mm command or other command to build your apk, the script myprepare.py will be invoked.

You can copy some files or do any thing python can do. But notice: don't add any print function in your python script.

[Refer] Empty parameter lists Thursday, September 15, 2011

C distinguishes between a function declared with an empty parameter list and a function declared with a parameter list consisting of only void. The former is an unprototyped function taking an unspecified number of arguments, while the latter is a prototyped function taking no arguments.

    // C code

    extern int  foo();          // Unspecified parameters
    extern int  bar(void);      // No parameters

    void baz()
    {
        foo(0);         // Valid C, invalid C++
        foo(1, 2);      // Valid C, invalid C++

        bar();          // Okay in both C and C++
        bar(1);         // Error in both C and C++
    } 

C++, on the other hand, makes no distinction between the two declarations and considers them both to mean a function taking no arguments.

    // C++ code

    extern int  xyz();

    extern int  xyz(void);  // Same as 'xyz()' in C++,
                            // Different and invalid in C 

For code that is intended to be compiled as either C or C++, the best solution to this problem is to always declare functions taking no parameters with an explicit void prototype. For example:

    // Compiles as both C and C++
    int bosho(void)
    {
        ...
    } 

Empty function prototypes are a deprecated feature in C99 (as they were in C89).

Refer to http://david.tribble.com/text/cdiffs.htm

do {} while (0) Friday, September 9, 2011

http://c2.com/cgi/wiki?TrivialDoWhileLoop

A demo using mmap to read a file Thursday, September 8, 2011

#include
  #include
  #include
  #include
  #include
  #include

  int main (int argc, char *argv[])
  {
          struct stat sb;
          off_t len;
          char *p;
          int fd;

          if (argc < 2) {
                  fprintf (stderr, "usage: %s \n", argv[0]);
                  return 1;
          }

          fd = open (argv[1], O_RDONLY);
          if (fd == -1) {
                  perror ("open");
                  return 1;
          }

          if (fstat (fd, &sb) == -1) {
                  perror ("fstat");
                  return 1;
          }

          if (!S_ISREG (sb.st_mode)) {
                  fprintf (stderr, "%s is not a file\n", argv[1]);
                  return 1;
          }

          p = mmap (0, sb.st_size, PROT_READ, MAP_SHARED, fd, 0);
          if (p == MAP_FAILED) {
                  perror ("mmap");
                  return 1;
          }

          if (close (fd) == -1) {
                  perror ("close");
                  return 1;
          }

          for (len = 0; len < sb.st_size; len++)
                  putchar (p[len]);

          if (munmap (p, sb.st_size) == -1) {
                  perror ("munmap");
                  return 1;
          }

          return 0;
  }

create_singlethread_workqueue

struct workqueue_struct *create_singlethread_workqueue(const char *name);

Creates a workqueue. Each workqueue has one dedicated processes ("kernel threads"), which run functions submitted to the queue.