I asked a really terrible question last time so I will try and do better here. I have the following code:
int main(int argc, char* argv[])
{
int forkChild;
char* argList[] = {"10","20","30"};
forkChild = fork();
if(forkChild == 0)
{
execvp("sleep",argList);
exit(0);
}
else
{
wait(NULL);
}
}
I am having trouble getting the execvp line to work. It will not sleep at all. It seems that the trouble might be because the argList array is passing strings and not integers to execvp. If I plug an integer directly into sleep it seems to work fine.
Eventually my program should be able to pass any parameter to execvp, so I am not sure why there is a problem with argument types. Is there something to this that I am not seeing?
Thanks
Related
My Code
#include<stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/wait.h>
int main()
{
char * arg_list[3];
arg_list[0] = "ls";
arg_list[1] = "-l";
arg_list[2] = 0;
char *arg_list2[3];
arg_list2[0] = " ps";
arg_list2[1] = "-ef";
arg_list2[2] = 0;
for(int i=0;i<5;i++){ // loop will run n times (n=5)
if(fork() == 0) {
if (i == 0){
execvp("ls", arg_list);
}else if(i==1){
execvp("ps" , arg_list2);
}else if(i>1){
printf("[son] pid %d from [parent] pid %d\n",getpid(),getppid());
exit(0);
}
}
}
for(int i=0;i<5;i++) // loop will run n times (n=5)
wait(NULL);
}
ME trying to modify it
#include<stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/wait.h>
int main()
{
for(int i=0;i<5;i++){ // loop will run n times (n=5)
if(fork() == 0) {
printf("[son] pid %d from [parent] pid %d\n",getpid(),getppid());
execlp(argv[i],argv[i],argv[i+1],(char*)NULL);
exit(0);
}
}
for(int i=0;i<5;i++) // loop will run n times (n=5)
wait(NULL);
}
-- NEED GUIDANCE AND UNDERSTANDING
I am trying to make my own tiny little shell program. When I run my first code works fine, runs all commands on the command line. But I cannot know and define all commands the user might enter. So i am trying to get a base code which could run any commands single or multiple entered by user. I tried using execlp where it does not compile saying argv is not defined which is true as i don't want to specifically define it.
I am trying to make my own tiny little shell program. When I run my first code works fine, runs all commands on the command line. But I cannot know and define all commands the user might enter.
For sure.... A shell program purpose is basically:
Read user input
Execute user input
Return result of execution.
There's nothing in your code that read user input....
So i am trying to get a base code which could run any commands single or multiple entered by user.
So read user input ;-)
I tried using execlp where it does not compile saying argv is not defined which is true as i don't want to specifically define it.
For sure ... but how would GCC guessed that `argv[]̀ must be automaticallty filled with user input ?
There's nothing automatic when coding in C language. You have to manage this manually.
Also, note that argc, argv et envp are usually reserved for main() function:
main(int argc, char **argv, char **envp)
So you may use something else to build your command array.
In pseudo code, what you must implement is:
quit=0
while (quit = 0) {
command_to_run = read_user_input();
if (command_to_run == "exit") {
quit = 1;
} else {
execute(command_to_run);
}
}
Some advices:
Try to use more functions. For example, implement a fork_and_run(char **cmd) function to fork and then execute command provided by the user. Il will make your code more readable and easy to maintain.
Read carefully manpages: everything you should know (like, for example, the fact that array provided to execvp() must be NULL-terminated) is written in it.
Your debugging messages should be printed to stderr. The result of the command run must be printed to stdin, so use fprintf() instead of printf() to write to the correct stream.
I would use a #define debug(x) fprintf(stderr, x) or something similar for debugging output so that you can easily disable later ;-)
I want to write a cmd script to periodically empty the working set from the command prompt. For now I empty the working set in the Rammap tool from sysinternals, but that can't be run by a script.
It's probably easiest to compile something like this:
#include <iostream>
#include <windows.h>
int main(int argc, char **argv) {
if (argc != 2) {
std::cerr << "Usage: min_mem <process_id>\n";
return 1;
}
HANDLE process = OpenProcess(PROCESS_SET_QUOTA, false, atoi(argv[1]));
SetProcessWorkingSetSize(process, -1, -1);
}
...and then run it in your script, something like:
mem_min 1234
...but replacing 1234 with the process ID (in decimal) of the process whose memory you want to minimize.
That said: I'd ask that this answer not be upvoted, since it's really a pretty crappy answer to a question that's basically just a gimme the codez I've been weak enough to post it, but would prefer not to get any rep for doing so.
I have following code:
int _tmain(int argc, char** argv) {
bool g_graphics = true;
palPhysics * pp = 0;
#ifndef PAL_STATIC
PF -> LoadPALfromDLL();
#endif
char a[] = "Bullet";
std::string aa;
aa = std::string(argv[1]);
//PF->SelectEngine("Bullet");
DebugBreak();
PF -> SelectEngine(argv[1]);
//PF->SelectEngine(aa);
//debug
// assert(false);
pp = PF -> CreatePhysics();
}
I am trying to read in the command line argument no. 1 in this line:
PF->SelectEngine(argv[1]);
However, I only get the first letter of the argument. I have also tried changing
int _tmain(int argc, char** argv)
to
int _tmain(int argc, TCHAR** argv), but then I get
error:
error C2664: 'palFactory::SelectEngine' : cannot convert parameter 1 from 'TCHAR *' to 'const PAL_STRING &'
PAL_STRING is just a std::string.
This might be a simple one, but I am not sure how to convert TCHAR to std::string, especially since TCHAR is something else depending on compiler /environment settings. Is anyone aware of an easy way to get the command-line arguments to work, such that I don't need to convert anything myself, i..e maybe by changing the tmain function?
Thanks!
C
Update: example of invoking on command line:
Yep. so the way I invoke this on command line is:
progname.exe arg1 arg2,
where arg1 is a physics engine I am trying to load, and arg2 is a dae(physics file with physics info), so I go, specifically:
progname.exe Bullet E:/a.dae
Stepping into the line "PF->SelectEngine(argv[1]);" gives the following code:
bool palFactory::SelectEngine(const PAL_STRING& name) {
#ifdef INTERNAL_DEBUG
printf("palFactory::SelectEngine: this = %p\n", this);
#endif
SetActiveGroup(name); // also calls RebuildRegistry
return isClassRegistered("palPhysics");
}
, in this case, when debugging, I can see that const PAL_STRING& name, i.e. the string, is just "B", instead of what I would expect it to be, which is "Bullet", my command line argument I have passed in the command line.
I've been plauged by this problem for years. The only solution I've been able to find is to NOT USE Visual Studio. I've had to fall back to using other compilers when I must be able to process command-line args. Specifically, I've been using the Digital Mars compiler successfully. It handles the command-line args correctly. I use the VS environment for intellisense and debugging, then compile with DMC to deploy.
---edit below---
Turns out, I just wasn't asking the right question. I finally asked the right question, and got the right answer! See link below.
What is the difference between _tmain() and main() in C++?
i try to compile this code:
#include <stdio.h>
void print(FILE *a)
{
int main();
int count=20;
int c;
int stop=0;
char answer;
while(!stop){
while((c=getc(a))!=EOF){
fprintf(stdout,"%c",c);
if(c=='\n'){
count--;
if(!count){
printf("do you want continue:y=for continue/q=for quit");
fflush(stdin);
answer=getchar();
if(answer=='y' || answer=='Y')
count=20;
else if(answer=='Q' || answer=='q'){
printf("you quit this program,press any key and hit the enter to close");
stop=1;
break;
}
else{
printf("argument is unacceptable,rolling back action");
main();
}
}
}
}
if(c==EOF)
stop=1;
}
}
void halt()/*do nothing just for halt and waiting for input*/
{
int a;
scanf("%d",&a);
}
int main()
{
FILE *in,*fopen();
char name1[25];
int a;
printf("enter the name of the file you want to show:");
scanf("%24s",name1);
in=fopen(name1,"r");
if(in==NULL){
printf("the files doesnt exist or it is in another directory, try to enter again\n");
main();
}
else
print(in);
fclose(in);
halt();
return 0;
}
the purpose of the program is to show 20 line content of a file. i compiled it in windows xp with lccwin32 and it works as expected. but problem arise when i change my os to linux (Ubuntu:pricise pangolin 12.04 LTS Desktop) and compile it with gcc.first it seems works fine but until the 20th line and prompt is out, when i put the argument (y for continue , q for quit)and hit the enter, but nothings happen. it just slipped away to elsepart which is starting again the program.so is it the gcc i have buggy or my code doesnt suit with gcc or may be i missed something?
I hate scanf. I would suggest replacing the scanf("%24s",name1) with fgets(s,24,stdin);
(And then unfortunately doing if (s[strlen(s)-1] == '\n') s[strlen(s)-1] = '\0' to get rid of the \n at the end.
I would also suggest:
Not use recursion on main
Use int main(int argc, char *argv[]) and then passing the name of your file as an argument (so you would check that argc > 1 and then use argv[1] as the filename, and then when running the program do ./programname filename)
Still not using scanf
In addition to the issues reported by #Foon you also have those problems :
fflush(stdin) is not working as you think it does.
scanf() leaves the newline character in the input buffer.
Your problem is that there is still a newline (\n) in the input buffer when you call getchar(), so your y/q answer is not even read.
Replacing fflush(stdin) with a solution from 1., or replacing fflush()+getchar() with scanf("\n%c",&answer); should solve that particular issue.
I'm new to Mathlink, and before integrating it in my code I tried to write a small REPL to get accustomed to it. The code is as follows (irrelevent parts omitted, and sorry for the horrible blend of C and C++):
int main(int argc,char **argv)
{
init_and_openlink(argc,argv);
while(!feof(stdin))
{
int pkt;
char buf[1024];
if(!fgets(buf,1024,stdin))
continue;
MLPutFunction(lp,"EnterTextPacket",1);
MLPutString(lp,buf);
MLEndPacket(lp);
while(((pkt=MLNextPacket(lp),pkt))&&(pkt!=RETURNPKT))
{
MLNewPacket(lp);
if(MLError(lp))
return 1;
}
const char *result;
MLGetString(lp,&result);
printf("%s\n",result);
MLReleaseString(lp,result);
}
return 0;
}
but it doesn't seem to work at all. I've tried replacing the while loop with a single MLNextPacket instruction but to no avail; I spent hours searching Mathlink documentation, but that one is a big mess! Where I'm doing it wrong?
The EnterTextPacket MathLink packet will make the kernel return the result wrapped in a ReturnTextPacket MathLink packet. Try changing the condition in your while loop to:
while(((pkt=MLNextPacket(lp),pkt))&&(pkt!=RETURNTEXTPKT))