Table of Contents

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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