Download Command Line Arguments and Processes in CMSC 212 – S05 and more Exams Computer Science in PDF only on Docsity!
Announcements
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Program #3 due today 8pm
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Exam #2– one week from today– April 12– same room as the 1
st^ exam (ARM 0131)
st^ exam (6:00-7:15)
- minimally comprehensive l^
Reading– for today’s lecture
- The remaining portions of Chapter 13
Command Line Arguments
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int main(void){
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int main(int argc, char *argv[]){– argc - number of arguments (including program name)– argv - array of command line arguments
- argv[0] - command invoked to start program• argv[n] -
n
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command line argument
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Example:% args -file myfile -help– argv[0] = “args"– argv[1] = "-file"– argv[2] = "myfile"– argv[3] = "-help"
Command Line Arguments -- Table Example
int debugFlag, limit;char *inputFileName;option
optionTable[] = {
{ "-debug", Flag, &debugFlag },{ "-file", StrParam, &inputFileName },{ "-limit", IntParam, &limit },
/* possible other options go here */
}; int optionCount = sizeof(optionTable)/sizeof(option);
Project 1B Using Table Driven Parsing
typedef struct {
char *name;int opCode;int numRegisters;int usesMem; } opInfo;
static opInfo opTable[] = {
{ "Load",
{ "Move",
{ "Store", 3, 1, 1 },{ "Add",
{ "Halt",
{ "Negate", 6, 1, 0 },{ "Branch", 7, 2, 1 },{ "Bnn",
{ "Input", 10, 1, 0 },{ "Output", 11, 1, 0 },{ "Data",
Creating New Processes
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Use fork system call– UNIX (and LINUX) specific– creates a new copy of the current process
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Function Prototype
int fork();
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returns twice• once from initial call• second time in a new process
- return value indicates which process is which
the "child" (new) process
the "parent" (original) process
the "parent", but not child was created (error case)
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ps– UNIX command to see the current list of processes
Learning About Other Processes
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Wait and waitpid system call^ –
#include
<sys/types.h>
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#include
<sys/wait.h>
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pid_t
wait(int
*status);
- wait until a child process terminates -^
pid_t
waitpid(pid_t
pid,
int
*status,
int
options);
- wait until the passed process terminates
- return is the id the the terminated process– status fills out a status variable
- WIFEXITED(status) - true if the child terminated normally• WEXITSTATUS(status) - low 8 bits of parameter to exit• WTERMSIG(status) - signal number that terminated process
Additional I/O system Calls
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Sometimes processes want to communicate– abstraction: pipe - one process writes, other reads what was written– shell example:
ls | wc -l
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int pipe(int filedes[2]);– create a pipe between two processes– write and read system call can use these
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Standard I/O– filedescriptor 0 is standard input to a process– filedescriptor 1 is standard output from a process– filedescriptor 2 is standard error output from
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int dup2(int oldfd, int newfd);– change output of one filedescriptor to another– dup2(fd, myfd)
- now all standard input comes from myfd
A Simple Shell Program
while (1) {
ret = fgets(line, sizeof(line), stdin);… /* convert line into array of arguments */pid = fork();if (pid == 0) {
ret = execvp(args[0], args); if (ret) {
printf("Command not found\n");exit(-1); } } else if (pid > 0) {
ret = waitpid(pid, &status, NULL); } else { … } }
