Understanding of Format Specifiers in C Language

Format specifiers in C language play a crucial role in informing the compiler about the data type to be printed or

scanned during input and output operations. These specifiers always start with a ‘%’ symbol and are utilized within formatted strings in functions like printf(), scanf(), sprintf(), and more.

C offers a range of format specifiers, each associated with different data types. For instance, ‘%d’ corresponds to int, ‘%c’ to char, and so on. This article will delve into some commonly used format specifiers and how to effectively use them. In programming, understanding and correctly using C format specifiers is crucial for precise data formatting and manipulation.

Commonly Used Format Specifiers in C

Here’s a list of the most frequently employed format specifiers in C:

Format Specifier	Description
%c	Char data type.
%d	Signed integer data type.
%e or %E	Scientific notation for floats.
%f	Float data type.
%g or %G	Float data type with current precision.
%i	Unsigned integer.
%ld or %li	Long data type.
%lf	Double data type.
%Lf	Long double data type.
%lu	Unsigned int or unsigned long.
%lli or %lld	Long long data type.
%llu	Unsigned long long.
%o	Octal representation.
%p	Pointer.
%s	String.
%u	Unsigned int.
%x or %X	Hexadecimal representation.
%n	Prints nothing.
%%	Prints the ‘%’ character.

Examples of Format Specifiers in C

1. Character Format Specifier – %c in C
   ‘%c’ is the format specifier for the char data type in C. It can be used for both formatted input and formatted output.

   #include <stdio.h>

   int main() {
       char c;
       // Using %c for character input
       scanf("Enter some character: %c", &c);
       // Using %c for character output
       printf("The entered character: %c", c);
       return 0;
   }

Input:

   Enter some character: A

Output:

   The entered character: A

2. Integer Format Specifier (signed) – %d in C
   ‘%d’ is used for signed integer input and output in C.

   #include <stdio.h>

   int main() {
       int x;
       // Taking integer input
       scanf("Enter the two integers: %d", &x);
       // Printing integer output
       printf("Printed using %%d: %d\n", x);
       printf("Printed using %%i: %3i\n", x);
       return 0;
   }

Input:

   Enter the integer: 45

Output:

   Printed using %d: 45
   Printed using %i:    45

3. Unsigned Integer Format Specifier – %u in C
   ‘%u’ is used for the unsigned integer data type. It also handles negative integer values by converting them to their first complement.

   #include <stdio.h>

   int main() {
       unsigned int var;
       scanf("Enter an integer: %u", &var);
       printf("Entered Unsigned Integer: %u", var);
       printf("Printing -10 using %%u: %u\n", -10);
       return 0;
   }

Input:

   Enter an integer: 25

Output:

   Entered unsigned integer: 25
   Printing -10 using %u: 4294967286

4. Floating-point Format Specifier – %f in C
   ‘%f’ is the floating-point format specifier for float data type. It’s used for input and output of floating-point numbers. ‘%e’ and ‘%E’ are also available for scientific notation.

   #include <stdio.h>

   int main() {
       float a = 12.67;
       printf("Using %%f: %f\n", a);
       printf("Using %%e: %e\n", a);
       printf("Using %%E, %E", a);
       return 0;
   }

Output:

   Using %f: 12.670000
   Using %e: 1.267000e+01
   Using %E, 1.267000E+01

5. Unsigned Octal Number for Integer – %o in C
   ‘%o’ is used to print or take input for unsigned octal integers.

   #include <stdio.h>

   int main() {
       int a = 67;
       printf("%o\n", a);
       return 0;
   }

Output:

   103

6. Unsigned Hexadecimal for Integer – %x in C
   ‘%x’ is used for hexadecimal integers, with lowercase alphabets in the representation. ‘%X’ is used for uppercase.

   #include <stdio.h>

   int main() {
       int a = 15454;
       printf("%x\n", a);
       printf("%X", a);
       return 0;
   }

Output:

   3c5e
   3C5E

7. String Format Specifier – %s in C
   ‘%s’ is used for printing strings or taking string inputs.

   #include <stdio.h>

   int main() {
       char a[] = "Hi Geeks";
       printf("%s\n", a);
       return 0;
   }

Output:

   Hi Geeks

Note: Using ‘%s’ with scanf() differs slightly, as it stops reading at whitespace. Scansets can be used to avoid this.

8. Address Format Specifier – %p in C
   ‘%p’ is used to print addresses and pointers in C.

   #include <stdio.h>

   int main() {
       int a = 10;
       printf("The Memory Address of a: %p\n", (void*)&a);
       return 0;
   }

Output:

   The Memory Address of a: 0x7ffe9645b3fc

Input and Output Formatting

C provides tools for formatting input and output. These tools are inserted between the ‘%’ sign and the format specifier symbol. Some common formatting options include:

• A minus (-) sign for left alignment.
• A number after ‘%’ specifies the minimum field width; if the characters are fewer, the remaining space is filled with spaces.
• A period (.) separates field width and precision.
• Precision sets the minimum number of digits in an integer, maximum characters in a string, or digits after the decimal point in a floating-point value.

Example of I/O Formatting:

“`c

include

int main() {
char str[] = “geeksforgeeks”;
printf(“%20s\n”, str);
printf(“%-20s\n”, str);
printf(“%20.5s\n”, str);