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strchr

Learn to search for a character in a string with strchr.

strchr: searching for a character

The strchr function finds the first occurrence of a specific character in a string. It comes with the <string.h> header. Its signature is char *strchr(const char *s, int c).

char *p = strchr("merhaba", 'a');
// p points at the first 'a'

If it cannot find the character, it returns NULL. Because the return value is a pointer, you compute the index by subtracting p - s. This gives the position from the start.

Computing the index from a pointer

strchr returns a pointer, not an index. To find the index, you subtract the start of the string.

char text[] = "merhaba";
char *p = strchr(text, 'a');
long index = p - text;
// index = 4

Here p holds the address of the first 'a'; text is the start of the array. The difference of two pointers gives the number of elements between them. This tells you the position. Always check whether p is NULL first.

Practice Print the index of the first 'a'

Use strchr to find the first 'a' in "merhaba dunya" and print its index with printf. You must include the <string.h> header to use strchr.

Starter code

main.c
#include <stdio.h>

int main(void) {
    char text[] = "merhaba dunya";
    /* Find the first 'a' position with strchr and print it */
    return 0;
}

Sample solution

main.c
#include <string.h>
char *p = strchr(text, 'a');
if (p != NULL) {
    printf("%ld\n", (long)(p - text));
}

Expected output

4

Questions and answers

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

1 What does strchr return if the character is not found?

  • NULL Correct answer
  • An empty string
  • 0
  • -1

Explanation: strchr returns NULL when nothing is found; it means an invalid pointer.

2 Fill in the blank: strchr call

Question 
char *p = ____(text, 'a');
Answer 
char *p = strchr(text, 'a');

Explanation: strchr searches for a character.

3 Match call to behavior

Term Meaning
strchr(s, c) First c position
p - s Index value
NULL Not found
char * Pointer type

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