- Preliminary:
- In printing,
C will view the
content of a
variable as
a (generic) sequence of bits
- C does not know (nor care) about the data type of the variable
- You must tell (instruct) C on how to interpret the bit pattern !!!
- In printing,
C will view the
content of a
variable as
a (generic) sequence of bits
- The printf() function
is used to print values of
all built-in data types
in C.
- Syntax of the printf()
function:
printf ( " format string " , value1, value2, ..... );The "format string" contains instructions on how to interpret each of the values in the parameter list
- Format string:
- The format string in the printf() function contains formatting characters that instruct the C compiler to print a value in the given format
- Commonly used formatting characters:
Formatting character Meaning %d Print the (next) value as a signed integer value %u Print the (next) value as a unsigned integer value %ld Print the (next) value as a long signed integer value %lu Print the (next) value as a long unsigned integer value %f Print the (next) value as a floating point value %lf Print the (next) value as a double precision floating point value %o Print the (next) value as a octal based number %x Print the (next) value as a hexadecimal based number %p Print the address as a hexadecimal based number %c Print the (next) value as a character (i.e., used the ASCII code) %s Print the (next) value as a string (will be explained much later) %% Print a % character
- Example:
int main( int argc, char* argv[] ) { int x; x = 'A'; printf( "x = 'A': %d, %u, %c\n", x, x, x); x = 64; printf( "x = 64: %d, %u, %c\n", x, x, x); x = -1; printf( "x = -1: %d, %u, %c\n", x, x, x); }Output:
x = 'A': 65, 65, A x = 64: 64, 64, @ x = -1: -1, 4294967295, (FFFF is not a printable chracater)
- Example Program:
(Demo above code)
- Prog file: /home/cs255001/demo/C/printf1-new.c
How to run the program:
- To compile: gcc printf1-new.c
- To run: ./a.out
- Warning:
- The C compiler do
not perform any
type checks in the
printf( ) function call
- Therefore, you must make sure that the data type of the variables correspond to formatting character
- The C compiler do
not perform any
type checks in the
printf( ) function call
- Example:
- Recall that
float uses the
IEEE 754 representation
- The representation for
2.0 is:
2.0(10) = 10.0(2) (binary) = 10.0(2) exp 0 = 1.0(2) exp 1 Stored Mantissa = .0000000000000000000000000 Stored Exponent = 01111111 + 1 = 10000000 (excess 127) The IEEE 754 representation of 2.0 is: 0 10000000 00000000000000000000000 Or: 01000000000000000000000000000000
- The statement:
float x = 2.0; printf("%d\n", x);will print absurd things....
- Recall that
float uses the
IEEE 754 representation
- Example Program:
(Demo above code)
- Prog file: click here
How to run the program:
- Right click on link and
save in a scratch directory
- To compile: gcc printf2.c
- To run: ./a.out