CS 2213 Advanced Programming
Input and Output

In C, a file pointer is a pointer to a structure of type FILE.
We are not concerned with the internal structure of this data type.

To create a file pointer from a file name, use the fopen function:

FILE *fopen(char *name, char *mode)

The second parameter is a short string that describes what you want to do with the file.
Here are the most-used options:

On some systems (not Unix) you need to also specify b as part of the mode string for binary files.

There are version of some of the functions we already know about that can be used for file I/O:

int getchar(void)	int getc(FILE *fp)
int putchar(int c)	int putc(int c, FILE *fp)
int printf(char *format, ...)	int fprintf(FILE *fp, char *format, ...)
int scanf(char *format, ...)	int fscanf(FILE *fp, char *format, ...)

You can use these new ones to do I/O to standard input and standard output without fopen by using the predefined file pointers stdin and stdout.

In fact, in some systems we have:

#define getchar() getc(stdin)
#define putchar(c) putc((c),stdout)

There is also another predefined file pointer called stderr.

When you are done with file I/O you should close the corresponding file with

int fclose(FILE *fp):

Example: concatenating files

The Unix command cat can take any number of command line parameters which are names of files.
The files are sent to standard output in the order they appear on the command line.
If no command line parameters are given, the input comes from standard input.

Example:
cat file1 file2 file3 > file4

Here is a simple version of cat

#include <stdio.h>
main (int argc, char *argv[]) {
   FILE *fp;
   void filecopy(FILE *, FILE *);

   if (argc == 1)
      filecopy(stdin,stdout);
   else
      while (--argc > 0)
         if ( (fp = fopen(*++argv, "r")) == NULL) {
            printf("cat: can't open %s\n",*argv);
            return 1;
         }
         else {
            filecopy(fp,stdout);
            fclose(fp);
         }
   return 0;
}
void filecopy(FILE *ifd, FILE *ofd) {
   int c;
   while (c=getc(ifp) != EOF)
      putc(c, ofp);
}

Error Handling --- stderr and exit

Another useful function is

int ferror(FILE *fp);

Here is another version of out cat

main (int argc, char *argv[]) {
   FILE *fp;
   void filecopy(FILE *, FILE *);
   char *prog = argv[0];

   if (argc == 1)
      filecopy(stdin,stdout);
   else
      while (--argc > 0)
         if ( (fp = fopen(*++argv, "r")) == NULL) {
            fprintf(stderr,"%s: can't open %s\n",prog,*argv);
            return 1;
         }
         else {
            filecopy(fp,stdout);
            fclose(fp);
         }
   if (ferror(stdout)) {
      fprintf(stderr,"%s: error writing stdout\n",prog);  
      return 2;
   }
   return 0;
}

Another useful function is exit which exits your program. This can be called from a function other than main.

In general you should avoid doing this unless absolutely necessary.

When called from main, exit(expr) does exactly the same thing as return expr.

Miscellaneous Functions

strcat(s,t)
strncat(s,t,n)
strcmp(s,t)
strncmp(s,t,n)
strcpy(s,t)
strncpy(s,t,n)
strlen(s)
strchr(s,c)     return a pointer to the first c in s or NULL
strrchr(s,c)    return a pointer to the last c in s or NULL

int atoi(const char *str);
double atof(const char *str);

Mathematical Functions
These are defined in math.h and you will need to add -lm to the end of your compile line.
All take double parameters and return double:

sin(x)
cod(x)
atan2(y,x)
exp(x)
log(x)
log10(x)
pow(x,y)
sqrt(x)
fabs(x)

typedef struct nodeentry {
   stringval sval;
   struct nodeentry *next;
   struct nodeentry *prev;
} nodeentry;

typedef struct {
   nodeentry *front;
   nodeentry *rear;
} doublelist;

int insert_after(stringval sval, nodeentry *nentryp);
int insert_before(stringval sval, nodeentry *nentryp);
stringval remove(nodeentry *nentryp);