#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <time.h>
#include <string.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/time.h>
#include <sys/resource.h>
#define MAX_INPUT_SIZE 128
extern char **environ;
//I moved the collection of research stats functionality to a separate method so that it can be used for either built in or external commands that are inputted
void get_resource_stats () {
struct rusage usage;
int status;
struct timeval start_time, end_time;
getrusage(RUSAGE_CHILDREN, &usage);
clock_t startCPUTime = clock();
time_t startWallClockTime = time(0);
wait(0);
clock_t endCPUTime = clock();
time_t endWallClockTime = time(0);
double cpuTime = (double) (endCPUTime - startCPUTime) / CLOCKS_PER_SEC * 1000; //cpu time in milliseconds using built in CLOCKS_PER_SEC constant
double wallClockTime = difftime (endWallClockTime, startWallClockTime) * 1000; //wall clock time in milliseconds using diffTime method call
printf("CPU time elapsed: %f ms\n", cpuTime);
printf("Wall clock time elapsed: %f ms\n", wallClockTime);
printf("Involuntary Preemptions: %ld\n", usage.ru_nivcsw);
printf("Voluntary Preemptions: %ld\n", usage.ru_nvcsw);
printf("Major Page Faults: %ld\n", usage.ru_majflt);
printf("Minor Page Faults: %ld\n", usage.ru_minflt);
printf("Maximum Resident Set Size: %ld kilobytes\n", usage.ru_maxrss);
}
void exec_commands (char *input) {
pid_t pid = fork();
if (pid < 0) {
fprintf(stderr, "Fork error\n");
exit(1);
} else if (pid == 0) {
char *command = strtok(input, " "); // Get the first token as the command
char *args[MAX_INPUT_SIZE];
int arg_count = 0;
while (command != NULL && arg_count < MAX_INPUT_SIZE - 1) {
args[arg_count++] = command;
command = strtok(NULL, " "); // Get the next token as an argument
}
args[arg_count] = NULL;
if (execvp(args[0], args) == -1) {
fprintf(stderr, "Execve error\n");
exit(1);
}
}
}
int main (int argc, char *argv[]) {
//shell input functionality
char input[MAX_INPUT_SIZE];
char prompt[MAX_INPUT_SIZE];
//initialize prompt with default arrow value
strcpy(prompt, "==> ");
// create child process with fork
int pid;
if (argc < 2) {
while (1) {
printf("%s", prompt);
if (fgets(input, sizeof(input), stdin) == NULL) {
// handle the end of the user input
printf("\n");
break;
}
//remove newline character at the end of input (enter key)
input[strlen(input) - 1] = '\0';
//built in commands (1) exit, (2) cd dir, or (3) set prompt!
if (strncmp(input, "exit", 4) == 0) {
break;
} else if (strncmp(input, "cd ", 3) == 0) {
//first 3 characters are "cd ", this finds and sets directory named after these three characters of input
char *new_dir = input + 3;
if (chdir(new_dir) !=0) {
fprintf(stderr, "cd error\n");
}
} else if (strncmp(input, "set prompt = ", 13) == 0) {
//strcpy can be used to copy new prompt to memory location of original prompt
//new prompt will start 11 characters into input, as first set of characters is "set prompt="
strcpy(prompt, input + 13);
printf("Your new prompt is: %s\n", prompt);
} else {
exec_commands(input);
get_resource_stats();
}
}
} else {
pid_t pid = fork();
if (pid < 0) {
fprintf(stderr, "Fork error\n");
exit(1);
} else if (pid == 0) {
char *command = argv[1];
char **arguments = &argv[1];
if((execvp(command,arguments)) == -1) {
fprintf(stderr, "Execve error\n");
exit(1);
}
} else {
get_resource_stats();
}
}
return(0);
} Write, Run & Share C Language code online using OneCompiler's C online compiler for free. It's one of the robust, feature-rich online compilers for C language, running the latest C version which is C18. Getting started with the OneCompiler's C editor is really simple and pretty fast. The editor shows sample boilerplate code when you choose language as 'C' and start coding!
OneCompiler's C online editor supports stdin and users can give inputs to programs using the STDIN textbox under the I/O tab. Following is a sample C program which takes name as input and print your name with hello.
#include <stdio.h>
int main()
{
char name[50];
printf("Enter name:");
scanf("%s", name);
printf("Hello %s \n" , name );
return 0;
}
C language is one of the most popular general-purpose programming language developed by Dennis Ritchie at Bell laboratories for UNIX operating system. The initial release of C Language was in the year 1972. Most of the desktop operating systems are written in C Language.
When ever you want to perform a set of operations based on a condition if-else is used.
if(conditional-expression) {
// code
} else {
// code
}
You can also use if-else for nested Ifs and if-else-if ladder when multiple conditions are to be performed on a single variable.
Switch is an alternative to if-else-if ladder.
switch(conditional-expression) {
case value1:
// code
break; // optional
case value2:
// code
break; // optional
...
default:
// code to be executed when all the above cases are not matched;
}
For loop is used to iterate a set of statements based on a condition.
for(Initialization; Condition; Increment/decrement){
// code
}
While is also used to iterate a set of statements based on a condition. Usually while is preferred when number of iterations are not known in advance.
while(condition) {
// code
}
Do-while is also used to iterate a set of statements based on a condition. It is mostly used when you need to execute the statements atleast once.
do {
// code
} while (condition);
Array is a collection of similar data which is stored in continuous memory addresses. Array values can be fetched using index. Index starts from 0 to size-1.
data-type array-name[size];
data-type array-name[size][size];
Function is a sub-routine which contains set of statements. Usually functions are written when multiple calls are required to same set of statements which increases re-usuability and modularity.
Two types of functions are present in C
Library functions are the in-built functions which are declared in header files like printf(),scanf(),puts(),gets() etc.,
User defined functions are the ones which are written by the programmer based on the requirement.
return_type function_name(parameters);
function_name (parameters)
return_type function_name(parameters) {
//code
}