Learning and summary based on pthread_create, readlink, getpid and other functions_jquery

pthread_create is a UNIX environment thread creation function

Specific format:
#include
　int pthread_create( pthread_t *restrict tidp,const pthread_attr_t *restrict attr,void*（*start_rtn)(void*),void *restrict arg);
Return value: If successful, return 0, otherwise return error number
On a successful return, the memory unit pointed to by tidp is set to the thread ID of the newly created thread. The attr parameter is used to specify various thread attributes. The newly created thread starts running from the address of the start_rtn function. This function has only one pointerless parameter arg. If more than one parameter needs to be passed to the start_rtn function, then these parameters need to be put into a structure, and then the address of this structure is used as The parameter arg is passed in.
Use C to develop multi-threaded programs under Linux. Multi-threading under the Linux system follows the POSIX thread interface, called pthread.

#include
int pthread_create(pthread_t *restrict tidp, const pthread_attr_t *restrict attr, void *(*start_rtn)(void), void *restrict arg);

Returns: 0 if OK, error number on failure

The pointer modified by restrict is the only way to initially access the object pointed to by the pointer. Only when the second The object can only be accessed when the pointer is based on the first one. Access to objects is restricted to pointer expressions modified by restrict. Pointers modified by restrict are mainly used for function parameters, or point to memory space allocated by malloc(). The restrict data type does not change the semantics of the program. The compiler can better optimize certain types of routines by making the assumption that a restrict-modified pointer is the only way to access an object.
The first parameter is a pointer to the thread identifier.
The second parameter is used to set thread attributes.
The third parameter is the starting address of the thread running function.
The last parameter is the parameter to run the function.
In addition, pay attention to adding the -lpthread parameter when compiling to call the static link library. Because pthread is not the default library of Linux system

====================================== ===========================================linuxAbout Readlink function Get the running path
Related functions: STAT, LSMLINK
Speed ​​head file: #include & lt; unistd.h & gt;
Define function: int readlink(const char *path, char *buf, size_t bufsiz);
Function description: readlink() will symbolically connect the parameter path The content is transferred to the memory space pointed to by parameter buf. The returned content is not terminated by NULL as a string, but the number of characters in the string is returned.If the parameter bufsiz is less than the content length of the symbolic link, the excessively long content will be truncated

Return value: If the execution is successful, the file path string pointed to by the symbolic link will be passed. If it fails, -1 will be returned. , The error code is stored in errno
Error code:
EACCESS EACCESS Retrieving the file was denied, the permissions are insufficient
EINVAL The parameter bufsiz is a negative number
EIO EIO Access error
ELOOP The file you want to open has a history Multi-symbol connection problem
ENAMETOOLONG The path name of parameter path is too long
ENOENT The file specified by parameter path does not exist
ENOMEM Insufficient core memory
ENOTDIR The directory in the path parameter exists but is not a real one Directory
Example 1:
#include
#include
#define PATH_MAX 1024
char * get_exe_path()
{
static char buf[PATH_MAX];
int i;
int rslt = readlink("/proc/self/exe", buf, PATH_MAX);
if (rslt < 0 || rslt >= PATH_MAX)
{
return NULL;
}
buf[rslt] = '/0';
for (i = rslt; i >= 0 ; i--)
{
printf("buf[%d] %c/n", i, buf);
if (buf == '/')
{
buf[i 1] = '/0';
break;
}
}
return buf;
}
int main(int argc, char ** argv)
{
printf("%s/n", get_exe_path());
return 0;
}

=============== ================================================== ==============

getpid Get the process identification code

Related functions: fork, kill, getpid　Header file: #include >
Function description:
　 getpid() is used to obtain the process identification code of the current process. Many programs use this value to create temporary files to avoid problems caused by the same temporary files.

Return value: The process identification code of the current process

Example:
#include main( )　
{
printf(“pid=%d/n”,getpid()); Must be the same*/ ========================================== =======================================





strrchr() function




Definition and usage The position of the last occurrence in the string, and returns all characters from this position in the string to the end of the string. If the specified character cannot be found, the function will return NULL.

  语法
  char *strrchr(char *str, char c);

  例子
  #include 　　
  #include 　　
  int main(void)　　
  　　char string[16];
  　　char *ptr, c = 'r';

  　　strcpy(string, "This is a string");
  　　ptr = strrchr(string, c);

  　　if (ptr)
  　　         printf("The character %c is at position: %d/n", c, ptr-string);
  　　else
  　　         printf("The character was not found/n");
  　　return 0;　　
  }　　

  运行结果是：The character r is at position：12

  ===============================================================================

  strstr（）函数用法
  
c 函数原型：
const char * strstr ( const char * str1, const char * str2 );
char * strstr ( char * str1, const char * str2 );

C函数原型：
char * strstr ( const char *, const char * );
a字符串里 查看是否有b字符串，
有则 从首次发现b字符串处 返回 a字符串。
没有则输出 null
例子:
char st[]="abc 1234 xyz";
printf("%s",strstr(st,"34") );

打印出：
34 xyz