I/O in C

Question 1

What are the “standard” streams?

Answer 1

• stdin - standard input
  
  • usually from input but can also be used when piping in unix
• stdout - standard output
  
  • usually to screen but can also be used when piping in unix
• stderr - standard error
  
  • usually to screen

note: #include <stdio.h> is required</stdio.h>

Question 2

What using scanf, what operater is needed?

Answer 2

& is needed for int, floar or char but not needed with strings

Question 3

How would you introduce error checking with scanf?

Answer 3

while(scanf(“%d”, &1) == 1){

//will loop while we have appropriate input

}

Question 4

How would you skip blank spaces or dashes in the input stream?

Answer 4

scanf(“%d %d %d”, &day, &month, &year);

scanf(“%d-%d-%d”, &day,&month,&year);

Question 5

How do you use fgets( ) and how do you specifify a maximum number of characters? How does this differ from fscanf( )? What does fscanf( ) return?

Answer 5

define MAX 81

char buffer[MAX];

fgets(buffer, MAX, stdin);

• reads from stdin, stores info in buffer up to the MAX-1 (it allows for the addition of the null terminating character)

fscanf( ) reads the whole line un buffered

• it returns the number of input items converted and assigned successfully

Question 6

How do you open a file in C?

List the read modes.

Answer 6

FILE * inputfile = NULL;

inputfile = fopen(“names.txt”, “r”);

Read Modes:

• r - read only
• w - write to (overwriting current file if there is one)
• a - appends to the file

Question 7

What are the basic file handling functions:

Answer 7

• fopen()
• fclose()
• fscanf()
• fprintf()

Question 8

How do you error check the opening of a file?

Answer 8

File handler becomes NULL when an fopen() occurs

if(inputfile == NULL)

{

printf(“Unable to open input file.\n”);

return 1;//ends program if inside main function

}

Question 9

How would you read a list of name from inputfile?

Answer 9

while(fscanf(inputfile, “%s”, name) == 1)

{

}

Question 10

How would you open a file to write to, and then write to it?

Answer 10

FILE *outfile = null;

outfile = fopen(“name.txt”, “w”);

if (fprintf(“%s\n”, name) <= 0){printf(“error writing to file”); return 1;}

fputs(char * s, * filehandler);

This will not only write to the file but error check it at the same time.

Question 11

How do you use:

1. fgets()
2. fputs()

Answer 11

1. char *fgets(char *s, int n, FILE * fp)
   
   1. reads an entire line into s, up to n-1 characters in length
   2. returns the point s on success or NULL if error or EOF is reached
   3. (‘\n’) stops reading but is included in the string
2. int fputs(char *s, FILE *fp);
   
   1. returns the number of characters written if successful, otherwise, return EOF