What is strchr()?

The strchr() function finds the first occurrence of a specific character in a string and returns a pointer to that position. If the character is not found, it returns NULL.

Header File

#include <string.h>

Syntax

char *strchr(const char *str, int c);

Parameter	Description
`str`	String to search in
`c`	Character to find (passed as int, treated as char)

Return Value

Return Value	Meaning
Pointer	Points to first occurrence of character
NULL	Character not found in string

Basic Examples

Example 1: Find First Occurrence

#include <stdio.h> #include <string.h> int main() { char str[] = "Hello World"; char *ptr = strchr(str, 'o'); if(ptr != NULL) { printf("Found 'o' at position: %ld\n", ptr - str); // 4 printf("From 'o' onward: %s\n", ptr); // o World } return 0; }

Example 2: Character Not Found

#include <stdio.h> #include <string.h> int main() { char str[] = "Hello"; char *ptr = strchr(str, 'z'); if(ptr == NULL) { printf("Character 'z' not found in '%s'\n", str); } return 0; }

Example 3: Finding Space Character

#include <stdio.h> #include <string.h> int main() { char sentence[] = "Cloud Computing is powerful"; char *space = strchr(sentence, ' '); if(space != NULL) { printf("First space at position: %ld\n", space - sentence); // 5 printf("First word: "); for(int i = 0; i < space - sentence; i++) { printf("%c", sentence[i]); // Cloud } printf("\n"); } return 0; }

Practical Examples

Example 4: Count Character Occurrences

#include <stdio.h> #include <string.h> int main() { char str[] = "programming"; char search = 'm'; int count = 0; char *ptr = str; while((ptr = strchr(ptr, search)) != NULL) { count++; ptr++; // Move to next character } printf("Character '%c' appears %d times in '%s'\n", search, count, str); // 2 times return 0; }

Example 5: Extract File Extension

#include <stdio.h> #include <string.h> int main() { char filename[] = "document.pdf"; char *dot = strchr(filename, '.'); if(dot != NULL) { printf("Filename: %s\n", filename); printf("Extension: %s\n", dot + 1); // pdf printf("Name without extension: "); for(int i = 0; i < dot - filename; i++) { printf("%c", filename[i]); // document } printf("\n"); } else { printf("No extension found\n"); } return 0; }

Example 6: Parse URL or Path

#include <stdio.h> #include <string.h> int main() { char url[] = "https://example.com/page.html"; // Find protocol separator char *colon = strchr(url, ':'); if(colon != NULL) { printf("Protocol: "); for(int i = 0; i < colon - url; i++) { printf("%c", url[i]); // https } printf("\n"); // Find domain after :// char *slash = strchr(colon + 3, '/'); if(slash != NULL) { printf("Domain: "); for(int i = colon + 3; i < slash - url; i++) { printf("%c", url[i]); // example.com } printf("\n"); printf("Path: %s\n", slash); // /page.html } } return 0; }

Example 7: Email Validation (Simple)

#include <stdio.h> #include <string.h> int main() { char email[] = "[email protected]"; char *at = strchr(email, '@'); if(at != NULL) { printf("Valid email format\n"); printf("Username: "); for(int i = 0; i < at - email; i++) { printf("%c", email[i]); // user } printf("\n"); printf("Domain: %s\n", at + 1); // example.com } else { printf("Invalid email - missing '@'\n"); } return 0; }

Example 8: Remove Trailing Newline

#include <stdio.h> #include <string.h> int main() { char input[100]; printf("Enter text: "); fgets(input, sizeof(input), stdin); // Find newline and replace with null terminator char *newline = strchr(input, '\n'); if(newline != NULL) { *newline = '\0'; } printf("You entered: '%s'\n", input); printf("Length: %lu\n", strlen(input)); return 0; }

Example 9: Split String at Character

#include <stdio.h> #include <string.h> int main() { char str[] = "Apple,Banana,Orange,Grape"; char *comma; printf("Original: %s\n", str); // Find first comma comma = strchr(str, ','); if(comma != NULL) { *comma = '\0'; // Replace comma with null terminator printf("First fruit: %s\n", str); // Apple printf("Remaining: %s\n", comma + 1); // Banana,Orange,Grape } return 0; }

Example 10: Find Multiple Characters

#include <stdio.h> #include <string.h> int main() { char str[] = "Hello World!"; char chars[] = "aeiou"; // vowels to find int found = -1; // Find first vowel in string for(int i = 0; chars[i] != '\0'; i++) { char *ptr = strchr(str, chars[i]); if(ptr != NULL) { int pos = ptr - str; if(found == -1 || pos < found) { found = pos; } } } if(found != -1) { printf("First vowel found at position %d: '%c'\n", found, str[found]); // 'e' at position 1 } return 0; }

strchr() vs Related Functions

Function	Purpose	Finds
`strchr()`	First occurrence	Character
`strrchr()`	Last occurrence	Character
`strstr()`	First occurrence	Substring
`strpbrk()`	First of any characters	Set of characters

Example: strchr vs strrchr

#include <stdio.h> #include <string.h> int main() { char str[] = "Cloud Computing Cloud"; char *first = strchr(str, 'C'); char *last = strrchr(str, 'C'); printf("String: %s\n", str); printf("First 'C': position %ld - %s\n", first - str, first); printf("Last 'C': position %ld - %s\n", last - str, last); return 0; } /* Output: First 'C': position 0 - Cloud Computing Cloud Last 'C': position 16 - Cloud */

Example: strchr vs strpbrk

#include <stdio.h> #include <string.h> int main() { char str[] = "Hello World!"; // strchr - finds single character char *space = strchr(str, ' '); printf("strchr space: %s\n", space); // " World!" // strpbrk - finds any character from set char *found = strpbrk(str, "aeiou"); printf("strpbrk vowel: %s\n", found); // "ello World!" return 0; }

Manual Implementation

#include <stdio.h> char *my_strchr(const char *str, int c) { while(*str != '\0') { if(*str == (char)c) { return (char*)str; // Found } str++; } // Check if searching for null terminator if(c == '\0') { return (char*)str; } return NULL; // Not found } int main() { char str[] = "Programming"; char *ptr1 = my_strchr(str, 'g'); char *ptr2 = my_strchr(str, 'z'); if(ptr1) printf("Found 'g': %s\n", ptr1); // "gramming" if(!ptr2) printf("'z' not found\n"); return 0; }

Finding Null Terminator (Special Case)

#include <stdio.h> #include <string.h> int main() { char str[] = "Hello"; // strchr can find null terminator char *end = strchr(str, '\0'); if(end != NULL) { printf("Null terminator at position: %ld\n", end - str); // 5 printf("String length: %ld\n", strlen(str)); // 5 } return 0; }

Common Use Cases

1. Check if Character Exists

if(strchr("yesno", 'y') != NULL) { printf("Character found\n"); }

2. Get Substring After Character

char *ptr = strchr(text, '@'); if(ptr) { char *domain = ptr + 1; // After @ }

3. Remove All Occurrences

#include <stdio.h> #include <string.h> void remove_char(char *str, char remove) { char *read = str; char *write = str; while(*read) { if(*read != remove) { *write = *read; write++; } read++; } *write = '\0'; } int main() { char text[] = "Hello World"; remove_char(text, 'o'); printf("%s\n", text); // Hell Wrld return 0; }

4. Validate Character Set

#include <stdio.h> #include <string.h> int main() { char password[] = "Pass123!"; char special[] = "!@#$%"; int has_special = 0; for(int i = 0; special[i]; i++) { if(strchr(password, special[i])) { has_special = 1; break; } } if(has_special) { printf("Password contains special character\n"); } else { printf("Password needs a special character\n"); } return 0; }

Common Mistakes

Mistake	Wrong Code	Correct Code
Forgetting header	No include	`#include <string.h>`
Wrong return type	`char c = strchr(str, 'a');`	`char *ptr = strchr(str, 'a');`
Modifying string literal	`strchr("Hi", 'H')[0] = 'h';`	Use array: `char str[]="Hi";`
Not checking NULL	`*strchr(str,'z')`	Check `if(ptr != NULL)`

Quick Reference

Task	Code
Find first 'x'	`char *p = strchr(str, 'x');`
Check if found	`if(p != NULL)`
Get position	`int pos = p - str;`
Get rest of string	`char *rest = p;`
Get before character	Copy up to `p - str` characters
Find null terminator	`strchr(str, '\0')`
Count occurrences	Loop with `p = strchr(p+1, c)`

Key Points

Returns pointer, not index position
NULL return means character not found
Case-sensitive - 'A' and 'a' are different
Can find null terminator '\0'
First occurrence only - use strrchr() for last
Modifies original string if you change the returned pointer's value
Efficient - single pass through string
Use if(ptr) to check non-NULL (equivalent to if(ptr != NULL))

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