Under Linux, the CPU usage of C language is

#include <stdio.h> #include <stdlib.h> #include <unistd.h> //header file struct occupy //declare an occupy Structure { char name [20]; //define a char type array name name has 20 elements unsigned int user; //define an unsigned int type of user unsigned int nice; //define an unsigned int Type of rare unsigned int system; //define an unsigned int type system unsigned int idle; //define an unsigned int type of idle }; float g_cpu_used; //define a global float type g_cpu_used int cpu_num; //Define a global int type cup_num void cal_occupy (struct occupy *, struct occupy *); //declare a typeless function cal_occupy contains two structure parameters void get_occupy (struct occupy *); //declare a typeless function Get_occupy contains a structure parameter int main () //main function start { struct occupy ocpu [10]; //define the occupy structure variable name is ocpu with 10 elements struct occupy ncpu [10]; //define the occupy structure variable The name is ncpu with 10 elements int i; //Define a local int variable i cpu_num = sysconf(_SC_NPROCESSORS_ONLN); //The system call returns the number of cpus assigned to cpu_num for(;;) //infinite loop { sleep(1 Waiting for 1 second get_occupy(ocpu); //call the get function to bring back the structure array for the first time sleep(1); //wait for 1 second get_occupy(ncpu); //call the get function to bring back the array of structures The second for (i=0; i<cpu_num; i++) //loop cpu_num-1 times { cal_occupy(&ocpu[i], &ncpu[i]); //call the cal function to bring back the array of structures Printf("%f \ ", g_cpu_used); //Print g_cpu_used usage is displayed in 6 decimal places} } } void cal_occupy (struct occupy *o, struct occupy *n)//contains two for the untyped cal function Pointer variables of the formal parameter structure type O and N { double od, nd; //define the double precision real variable od, nd double id, sd; //define the double precision real variable id, sd double scale; Define a double-precision real variable scale od = (double) (o->user + o->nice + o->system +o->idle);//first time (user+priority+system + idle) time is assigned to od nd = (doub Le) (n->user + n->nice + n->system +n->idle);//Second time (user + priority + system + idle) time is assigned to od scale = 100.0 /(float)(nd-od); //100 except for the cast (nd-od) difference is the float type and then assigned to the scale variable id = (double) (n->user - o-> User); //The difference between the first time and the second time of the user is then assigned to id sd = (double) (n->system - o->system);//system first and second time The difference in time is then assigned to sd g_cpu_used = ((sd+id)*100.0)/(nd-od); //((user + system)乖100) except (the first and second time difference) Assigned to g_cpu_used } void get_occupy (struct occupy *o) //The pointer to the untyped get function contains a formal parameter structure class O { FILE *fd; //Define the file pointer fd int n; //Define the local variable n Int type char buff[1024]; //Define the local variable buff array to char type size is 1024 fd = fopen ("/proc/stat", "r"); //Open the stat file in R read mode Then assign the pointer fd fgets (buff, sizeof(buff), fd); //read the string of length buff from the fd file and save it to the starting place. The address is buff in this space for (n = 0; n < cpu_num; n + +) //loop cpu_num -1 times { fgets (buff, size of (buff), fd); //read the length of buff from the fd file The string is saved to the starting address in the buff space. /* The following is the result of converting the buff string into the corresponding structure parameter according to the parameter format. */sscanf (buff, "%s %u %u %u %u", &o[n].name, &o[n].user, &o[n].nice,&o[n].system, &o[n] .idle); /*The following is the wrong output */fprintf (stderr, "%s %u %u %u %u\ ", o[n].name, o[n].user, o[n ].nice,o[n].system, o[n].idle); } fclose(fd); //close the file fd }