Working with the Unix OS

C Libraries
}
switch (pid=fork()){
case 0: /* child exec's shell */
execl("/bin/sh","sh","-c",command,0);
/* fall through if exec fails */
case -1:
/* could not fork, print error message*/
perror(myname);
exit(1);
default: /* parent waits for child to finish */
while ((wval=wait(&status)) != pid)
if (wval == -1) return -1;
}
return status;
Buffer control
#include
char outbuf[BUFSIZ];
main()
{
int c; /* for no buffering */
}
setbuf(stdout, outbuf); /*set outbuf to NULL*/
while ((c=fgetc(stdin)) != EOF)
fputc(c, stdout);
The C Preprocessor
#include
#include "filename"
or
#include
for including files of text into a program
from current directory
from directory "/usr/include"
cc -I../include prog.c to change default directory redefine for defining constants
#define NUMLINES 60
#define
#define min(a,b)
for defining powerful in-line macros
((a) > (b) ? (a) : (b))
#if, #ifdef, #ifndef & #undef for managing conditional compilation
#define DEBUG
#ifdef DEBUG
printf("MyProg Version 1.0 (debug)\n"),
#else
printf("Myprog Version 1.0 (production)\n");
#endif
#undef __TURBOC__
#ifndef __TURBOC__
system("grep name * > names");
#endif
#if COLUMNS > 80
/* code for wide printers */
#else
/* code for narrow printers */
#endif
cc -DLINELENGTH=80 prog.c to define constants
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