Working with the Unix OS

C Libraries
/* cat.c: – concatenate files */
#include
main(int argc, char *argv[])
{
FILE *fp;
void filecopy(FILE *, FILE *);
char *prog=argv[0]; /* program name for errors */
}
if (argc == 1) /* no args; copy standard input */
filecopy(stdin, stdout);
else
while (--argc > 0)
if ((fp=fopen(*++argv,"r")) == NULL)
{
fprintf(stderr, "%s: can't open %s\n", prog, *argv);
exit(1);
}
else
{
filecopy(fp, stdout);
fclose(fp);
}
if (ferror(stdout))
{
fprintf(stderr,"%s: error writing stdout\n", prog);
exit(2);
}
exit(0);
Line Input and Output
/* getline.c: – read a line, return length*/
#include
int getline(char *line, int max)
{
if (fgets(line, max, stdin) == NULL)
return 0;
else
return strlen(line);
}
Read and writing to strings is similar to files
int sprintf(char *string, char *format, arg1, arg2, ...);
int sscanf(char *string, char *format, argl, arg2, ...);
Storage Management
#include
The functions malloc and calloc obtain blocks of memory dynamically.
void *malloc(size t n); /* pointer to n bytes */
void *calloc(size t n, size t size); /* n objects */
int *ip;
ip = (int *) calloc (n, sizeof(int));
void free(char *ptr) /* deallocate memory */
char *realloc(char *ptr, unsigned size)
/* preserve contents and change size */
/* dynamic expanding of arrays */
for (p=head; p!=NULL; p=p->next){
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