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In C programming, strings are arrays of characters terminated by a null character (\0). This special character indicates the end of the string, distinguishing it from other data arrays. C provides a set of standard library functions to handle strings, which are included in the header file <string.h>.
String Basics
Declaration and Initialization
Strings in C can be declared in several ways:
1. Character array:
char str1[6] = {'H', 'e', 'l', 'l', 'o', '\0'};
2. String literal:
char str2[] = "Hello";
String Termination
All C strings are terminated by a null character (\0), which allows functions to determine the end of the string.
String Handling Functions
strlen()
- Purpose: Returns the length of the string (number of characters before the null character).
- Syntax:
size_t strlen(const char *str); - Example:
char str[] = "Hello";
size_t len = strlen(str); // len will be 5
strcpy()- Purpose: Copies one string into another.
- Syntax:
char *strcpy(char *dest, const char *src); - Example:
char src[] = "Hello";
char dest[6];
strcpy(dest, src); // dest now contains "Hello"
strncpy()- Purpose: Copies up to
ncharacters from one string to another. - Syntax:
char *strncpy(char *dest, const char *src, size_t n); - Example:
- Purpose: Copies up to
char src[] = "Hello, World!";
char dest[6];
strncpy(dest, src, 5);
dest[5] = '\0'; // dest now contains "Hello"
strcat()- Purpose: Concatenates (appends) one string to the end of another.
- Syntax:
char *strcat(char *dest, const char *src); - Example:
char dest[12] = "Hello";
char src[] = " World";
strcat(dest, src); // dest now contains "Hello World"
strncat()- Purpose: Appends up to
ncharacters from one string to another. - Syntax:
char *strncat(char *dest, const char *src, size_t n); - Example:
- Purpose: Appends up to
char dest[12] = "Hello";
char src[] = " World!";
strncat(dest, src, 6); // dest now contains "Hello World"
strcmp()- Purpose: Compares two strings lexicographically.
- Syntax:
int strcmp(const char *str1, const char *str2); - Example:
char str1[] = "Hello";
char str2[] = "World";
int result = strcmp(str1, str2); // result will be negative because "Hello" < "World"
strncmp()- Purpose: Compares up to
ncharacters of two strings. - Syntax:
int strncmp(const char *str1, const char *str2, size_t n); - Example:
- Purpose: Compares up to
char str1[] = "Hello";
char str2[] = "Heaven";
int result = strncmp(str1, str2, 2); // result will be 0 because the first two characters are equal
strchr()- Purpose: Finds the first occurrence of a character in a string.
- Syntax:
char *strchr(const char *str, int c); - Example
char str[] = "Hello, World!";
char *ptr = strchr(str, 'o'); // ptr points to the first 'o' in "Hello, World!"
strrchr()- Purpose: Finds the last occurrence of a character in a string.
- Syntax:
char *strrchr(const char *str, int c); - Example:
char str[] = "Hello, World!";
char *ptr = strrchr(str, 'o'); // ptr points to the last 'o' in "Hello, World!"
strstr()- Purpose: Finds the first occurrence of a substring in a string.
- Syntax:
char *strstr(const char *haystack, const char *needle); - Example:
char str[] = "Hello, World!";
char *ptr = strstr(str, "World"); // ptr points to the start of "World" in "Hello, World!"
strtok()- Purpose: Splits a string into tokens based on delimiters.
- Syntax:
char *strtok(char *str, const char *delim); - Example:
char str[] = "Hello, World!";
char *token = strtok(str, ", "); // token will be "Hello"
while (token != NULL) {
printf("%s\n", token);
token = strtok(NULL, ", "); // next tokens will be processed
}
Example Program
Here’s a complete example program demonstrating the use of some of these functions:
#include <stdio.h>
#include <string.h>
int main() {
char str1[20] = "Hello";
char str2[] = "World";
// String length
printf("Length of str1: %lu\n", strlen(str1));
// String copy
strcpy(str1, str2);
printf("str1 after strcpy: %s\n", str1);
// String concatenation
strcat(str1, " Again");
printf("str1 after strcat: %s\n", str1);
// String comparison
int cmp = strcmp(str1, str2);
if (cmp == 0) {
printf("str1 and str2 are equal\n");
} else if (cmp < 0) {
printf("str1 is less than str2\n");
} else {
printf("str1 is greater than str2\n");
}
// Find character in string
char *ch = strchr(str1, 'W');
if (ch != NULL) {
printf("Character 'W' found at position: %ld\n", ch - str1);
} else {
printf("Character 'W' not found\n");
}
// Tokenizing string
char str3[] = "Hello, World! Welcome to C programming.";
char *token = strtok(str3, " ");
while (token != NULL) {
printf("Token: %s\n", token);
token = strtok(NULL, " ");
}
return 0;
}
Conclusion
Strings in C are a fundamental concept, and understanding how to manipulate them using the standard library functions is essential for effective C programming. The functions provided by <string.h> allow for a wide range of operations, from simple copying and concatenation to more complex searching and tokenizing tasks.
