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sscanf

Learn to read values from a string with sscanf.

sscanf: formatted reading from a string

The sscanf function works like scanf but reads from a string instead of the keyboard. It comes with the <stdio.h> header. Its signature is int sscanf(const char *s, const char *fmt, ...).

char input[] = "Ali 25";
char name[16];
int age;
int n = sscanf(input, "%s %d", name, &age);
// n = 2, name = "Ali", age = 25

The return value is the number of fields successfully read. Because name is a string, it is passed directly; age is an int so its address is passed as &age. This is a powerful tool to parse structured text.

Parsing name and age with sscanf

sscanf can extract multiple values from a string. The format string describes how each part is read.

char input[] = "Ayse 30";
char name[16];
int age;
sscanf(input, "%s %d", name, &age);
printf("%s %d\n", name, age);
// "Ayse 30"

Here %s reads up to the next space into name, and %d reads the number into age. The &age address operator gives the location of age in memory so that sscanf can write its value there. A string is passed by name because the name itself is already an address.

Practice Parse name and age

Use sscanf to read a name string and an age integer from "Alex 25". Then print n, name and age with printf using the "%d %s %d\n" format.

Starter code

main.c
#include <stdio.h>

int main(void) {
    char input[] = "Alex 25";
    /* Define name and age; read with sscanf; print with printf */
    return 0;
}

Sample solution

main.c
char name[16];
int age;
int n = sscanf(input, "%s %d", name, &age);
printf("%d %s %d\n", n, name, age);

Expected output

2 Alex 25

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 What does the sscanf call return?

  • The number of matched fields Correct answer
  • The number of characters written
  • An error code
  • A pointer

Explanation: sscanf returns the number of fields successfully read.

2 Match function to source

Term Meaning
sscanf Reads from a string
scanf Reads from the keyboard
%s %d Reads two fields
return Match count

3 Fill in the blank: sscanf call

Question 
int n = ____(input, "%s %d", name, &age);
Answer 
int n = sscanf(input, "%s %d", name, &age);

Explanation: sscanf reads from a string.

All lessons in Beginner

1 C basics

  1. What is C?
  2. Your first program
  3. Compile and run
  4. Comments
  5. printf and escapes
  6. Summary - C basics

2 Variables

  1. Declaring variables
  2. Variable assignment
  3. const
  4. Variable scope
  5. typedef
  6. Summary - Variables

3 Data types

  1. Integer types
  2. Floating-point types
  3. char
  4. sizeof
  5. Type conversion
  6. Summary - Data types

4 Project: Calculator

  1. Project design
  2. Add and subtract
  3. Multiply and divide
  4. Menu loop
  5. Putting it together

5 Operators

  1. Arithmetic operators
  2. Assignment operators
  3. Comparison operators
  4. Logical operators
  5. Bitwise operators
  6. Summary - Operators

6 I/O

  1. printf formatting
  2. scanf
  3. Multiple inputs
  4. getchar and putchar
  5. puts and fputs
  6. Summary - I/O

7 Conditionals

  1. The if statement
  2. else and else if
  3. The switch statement
  4. The ternary operator
  5. Nested conditionals
  6. Summary - Conditionals

8 Loops

  1. The for loop
  2. The while loop
  3. The do-while loop
  4. break and continue
  5. Nested loops
  6. Summary - Loops

9 Project: Shopping cart

  1. Cart design
  2. Adding products
  3. Calculating totals
  4. Listing the cart
  5. Putting it together

10 Arrays

  1. Declaring arrays
  2. Array access
  3. Array size
  4. Multidimensional arrays
  5. Arrays and loops
  6. Summary - Arrays

11 Strings

  1. String basics
  2. String literals
  3. strlen
  4. strcpy and strcat
  5. strcmp
  6. Summary - Strings

12 Functions

  1. Defining functions
  2. Return values
  3. Parameters
  4. Function prototypes
  5. Recursion
  6. Summary - Functions

13 Pointer basics

  1. What is a pointer?
  2. The & address operator
  3. Pointer dereference
  4. NULL
  5. Pointer arithmetic
  6. Summary - Pointer basics

14 Arrays and pointers

  1. Array name as pointer
  2. Pointer to array
  3. Passing arrays to functions
  4. Pointer loop
  5. Multidim array pointer
  6. Summary - Arrays and pointers

15 Project: To-do CLI

  1. Task model
  2. Adding tasks
  3. Listing tasks
  4. Completing tasks
  5. Putting it together

16 String functions

  1. strchr
  2. strstr
  3. strtok
  4. sprintf
  5. sscanf
  6. Summary - String functions

17 Structs

  1. Defining structs
  2. Using structs
  3. typedef struct
  4. Array of structs
  5. Nested structs
  6. Summary - Structs

18 Memory and stack

  1. Stack and heap
  2. Automatic storage
  3. malloc
  4. free
  5. calloc and realloc
  6. Summary - Memory and stack

19 Preprocessor

  1. #define
  2. #include
  3. Conditional compilation
  4. Macro functions
  5. Header files
  6. Summary - Preprocessor

20 Beginner final

  1. Project design
  2. Data model
  3. Functions
  4. Memory management
  5. Putting it together