Input/Output

From <stdio.h>

printf

int printf( const char *format, arg0,…,argN )

• If printing fails, the value -1 is returned

• otherwise, it returns the number of characters printed (i.e., the number of characters that make up the printed string)

printf("string_with_format_specifiers", variables_associated_to_specifiers)

• string_with_format_specifiers: formatted string is sent to the screen (stdout)

• The specifiers within the string are replaced by their corresponding associated values

Format specifiers

%[param_no$][flags][width][.precision]conversion

[param_no$] It allows specifying which variable to associate with a format specifier (based on the order in which the variables are passed).

Valid only on systems based on the POSIX standard

[flags]

Flag	Description
-	Left-aligned
+	Add the + symbol for positive values
' '	Add a space for positive values
0	Pad with 0 at the beginning
#	Always print the decimal point, even if there are no digits after it (only for float and double)

[width] Number of characters that should be written for that particular format specifier

[.precision] In the case of float and double, it specifies the number of digits after the decimal point

conversion | s | char[] | string | | c | char | character | | d,i | short, int, long, long long, char | signed integer in decimal notation. Add l for long and ll for long long | | u | short, int, long, long long, char | unsigned integer in decimal notation. Add l for long and ll for long long | | x | short, int, long, long long, char | integer in hexadecimal notation (x lowercase, X uppercase) | | e | float, double | decimal number in exponential notation | | f | float, double | decimal number in decimal notation | | a | float, double | decimal number in hexadecimal fractional notation with base-2 exponent (a lowercase, A uppercase) | | p | pointer | memory address stored in a pointer |

scanf

int scanf(const char *format, arg0, …, argN )

It returns the number of values (among those specified) that were actually read by the method from stdin

scanf("string_with_format_specifiers",variables_associated_to_specifiers_addresses)

• The input to stdin must be a string formatted as string_with_format_specifiers

• The values entered in the positions occupied by the specifiers within the string must respect both the format of the string and the type of the specifier

• The values corresponding to the specifiers are assigned to the variables whose addresses are passed to scanf

• Whitespace characters (space, tab, etc.) are, in most cases, ignored

• There is no concept of precision in numeric conversion

Format Specifiers

%[width].conversion

• [width]: maximum number of characters that must be written for that particular specifier

Examples

int m,n;
float f;
scanf("%d%f&d", &m, &f, &n);

If the user inserts 10.3 4 6 as input, the scanf interprets:

• m = 10

• f = 0.3

• n = 4

if (scanf("%d", &num) != 1)				
{ 				
     /* Display error message. */				
}

If a value in decimal format is not provided as input, an error message is displayed.

sprintf

int sprintf( char* s, const char *format, arg0, …, argN)

• Populates the string format with the variables arg0,...,argN and writes it in the string s

• Returns the number of characters written to s (excluding the null terminator)

sscanf

int sscanf( char* s, const char *format, arg0, …, argN)

• Reads input from the string s

• Returns the number of specified variables read from s and stored

getchar

int getchar(void)

• Reads a character from stdin and returns it

• If there is a read error (stdin error), it returns EOF

putchar

int putchar(int c)

• Sends the character c to stdout and returns the character written

• If there is a write error (stdout error), it returns EOF

gets

char *gets(char *s)

• Reads a full line from the keyboard via stdin

• Returns the read line in s (the newline character is not included in the string)

• If there is a read error (stdin error), it returns NULL

puts

int puts(const char *s)

• Sends the string s to stdout (with the addition of a newline )

• Returns a non-negative number if the write is successful

• If there is a write error (stdout error), it returns EOF