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.

Exercise 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.

Show example solution

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

Test yourself

What does the sscanf call return?
- The number of matched fields
- The number of characters written
- An error code
- A pointer
Show answer

The number of matched fields — sscanf returns the number of fields successfully read.
Match function to source

sscanf

Reads from a string
scanf

Reads from the keyboard
%s %d

Reads two fields
return

Match count

Fill in the blank: sscanf call

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

Show answer

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

Next lesson: Summary - String functions

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