c++ - creating file for shell output redirection -


this school assignment.

so have written c code shell handles terminating command &, , input / output redirection using > or <. using pipes , fork(), execvp().

the problem input/output redirection handles files already exist.

what need know how go redirecting output file doesn't exist - know have create file, i'm not sure how works.

for example: ls -a < test.txt

if test.txt not in directory, need create , redirect output that. how create file?

here basic example code not create new file:

        else if( '>' ==  buff[i] ){            i++;            j=0;             if( ' ' == buff[i] )                i++;             while( ' ' != buff[i] && < len )               out_file[j++]=buff[i++];            out_file[j]='\0';              if ( ( ofd = open(out_file,1) ) < 0 ){               perror("output redirected file");               exit( 1 );            }             close(1);            dup(ofd);         }

any how can output , create new file appreciated! thanks!

you need tell open create file, if necessary:

if ( ( ofd = open(out_file, o_wronly | o_creat) ) < 0 ) {

note code more readable if use named constants flags open. compare functionally equivalent

if ( ( ofd = open(out_file, 513) ) < 0 ) {

or even

if ( ( ofd = open(out_file, 0x0201) ) < 0 ) {

Comments

Post a Comment

Popular posts from this blog

iphone - Three second countdown in cocos2d -

i trying have 3 second countdown display when level beat in game. did: -(void) gamesegmentbeat { [self pauseschedulerandactions]; // overlay game opaque background ccsprite *opaquebg = [ccsprite spritewithfile:@"background1.png"]; opaquebg.position = screencenter; [self addchild:opaquebg z:10000]; // these 3 labels 3 seconds cclabelttf *three = [cclabelttf labelwithstring:@"3" fontname:@"helvetica" fontsize:100]; three.position = ccp(screencenter.x, screencenter.y); cclabelttf *two = [cclabelttf labelwithstring:@"2" fontname:@"helvetica" fontsize:100]; two.position = ccp(screencenter.x, screencenter.y); cclabelttf *one = [cclabelttf labelwithstring:@"1" fontname:@"helvetica" fontsize:100]; one.position = ccp(screencenter.x, screencenter.y); // secondspast specified in update method secondspast = 0; if (secondspast == 1) { [self addchild:thr...
Read more

hyperlink - how to do url routing in php -

sorry, don't know should exact technical term problem statement title of thread might misleading/confusing. that's reason why not able search problem solution on google. okay, i'm developing simple social network users. want each user have own profile link. for example, if username of user 'xyz' profile link should ' http://example.com/user/xyz now how create "virtual" link? edit: okay, learned it's mod_rewrite , got similar question how dynamically rewrite url facebook routes php delicate matter. mod_rewrite can in beginning, after becoming mess , f*** rather help, when "big" software needs scalable. remembering "routes" not part of specific application, nomenclature "server" interprets request "client" , returns specific value "client" configuration of request. ie, "router" server. what recommend study http protocol, rest , on. this surely in many things, knowi...
Read more

c - Avoiding Extra Malloc in Linked List (node->next = NULL) -

in linked list, i'm trying avoid malloc ing node without adding bunch of if statements , such. have following: polynomial create() { polynomial head = null; polynomial temp = null; int numterms, coefficient, exponent; int counter = 0; printf("enter number of terms in polynomial: "); scanf ("%d", &numterms); printf("\n"); if (numterms == 0) { head = malloc(sizeof(term)); head->coef = 0; head->exp = 0; head->next = null; return head; } while (numterms != counter) { // ask input printf("enter coefficient , exponent of term %d: ", (counter + 1)); scanf("%d %d", &coefficient, &exponent); printf("\n"); // create term if (temp == null) temp = malloc(sizeof(term)); temp->coef = coefficient; temp->exp = exponent; temp->next = null; //if((numterms - 1) != counter) tem...
Read more