C Programming Data Structures String Manipulation And Character Arrays Complete Guide

C Programming: Data Structures - String Manipulation and Character Arrays

Character Arrays

Character arrays in C are essentially sequences of characters used to store strings. A string in C is a series of characters terminated by a null character ('\0'). For instance:

char str[10] = "Hello";

In this example, the string "Hello" is stored in str, and C automatically adds the null character at the end, making the total array length 6.

String Initialization

Strings can be initialized in various ways:

char str1[] = "Hello";    // Automatically allocates 6 characters
char str2[6] = "Hello";   // Explicitly allocates 6 characters
char str3[6] = {'H', 'e', 'l', 'l', 'o', '\0'};  // Manual Initialization

Important Library Functions

The C Standard Library provides a set of functions for string manipulation, which are defined in string.h.

1. strlen(): Calculates the length of a string (excluding the null termination character).

   #include <stdio.h>
   #include <string.h>
   
   int main() {
       char str[] = "Hello";
       printf("Length: %lu\n", strlen(str));
       return 0;
   }
   

2. strcpy(): Copies a string from one character array to another.

   #include <stdio.h>
   #include <string.h>
   
   int main() {
       char src[] = "Hello";
       char dest[10];
       strcpy(dest, src);
       printf("Copied String: %s\n", dest);
       return 0;
   }
   

3. strncpy(): Copies a specified number of characters from a string to another array.

   strncpy(dest, src, n);   // Copy up to n characters from src to dest
   dest[n] = '\0';          // Manually terminate the destination string
   

4. strcat(): Concatenates two strings.

   #include <stdio.h>
   #include <string.h>
   
   int main() {
       char src[] = "World";
       char dest[15] = "Hello ";
       strcat(dest, src);
       printf("Concatenated String: %s\n", dest);
       return 0;
   }
   

5. strncat(): Appends a specified number of characters from one string to another.

   strncat(dest, src, n);   // Append up to n characters from src to dest
   

6. strcmp(): Compares two strings lexicographically.

   int result = strcmp(str1, str2);
   if (result == 0) 
       printf("Strings are equal");
   else if (result < 0)
       printf("str1 is less than str2");
   else
       printf("str1 is greater than str2");
   

7. strncmp(): Compares a specified number of characters from two strings.

   int result = strncmp(str1, str2, n);
   

8. strchr(): Finds the first occurrence of a specified character in a string.

   char *pos = strchr(str, ch);
   if (pos) 
       printf("Character found at position: %ld\n", pos - str + 1);
   else 
       printf("Character not found\n");
   

9. strstr(): Finds the first occurrence of a substring within a string.

   char *pos = strstr(haystack, needle);
   

String Input and Output

For input and output operations, the C Standard Library provides functions like gets(), puts(), scanf(), printf(), and fgets()/fputs(). However, caution is advised with gets() and scanf("%s") as they can lead to buffer overflow vulnerabilities. Instead, fgets() and fscanf() are safer alternatives for handling input.

// Using scanf for string input
scanf("%s", str);  // Vulnerable to buffer overflow

// Using fgets for safer string input
fgets(str, sizeof(str), stdin);  // Truncates input if it exceeds buffer size and includes newline
str[strcspn(str, "\n")] = '\0';  // Remove newline character if present

Handling Special Characters

Special characters and escape sequences like \n, \t, \\, and \" are often used in strings. They represent newline, tab, backslash, and double quotes respectively. For instance:

char str[] = "Hello\nWorld";
printf("%s", str);  // Outputs: 
// Hello
// World

char path[] = "C:\\Program Files\\";
printf("%s", path);  // Outputs: C:\Program Files\

Memory Management

When dealing with strings dynamically (using malloc(), calloc(), and realloc()), ensure proper memory allocation and deallocation to prevent memory leaks.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main() {
    char *str = (char *)malloc(10 * sizeof(char));
    if (str == NULL) {
        printf("Memory allocation failed\n");
        return 1;
    }
    strcpy(str, "Hello");
    printf("String: %s\n", str);
    free(str);  // Free the allocated memory
    return 0;
}

Understanding these concepts and techniques is crucial for proficient string manipulation in C programming. By leveraging character arrays and the functions from the C Standard Library, developers can handle text data efficiently and effectively in their applications.

Important Keywords

• String
• Character Arrays
• String manipulation
• String initialization
• string.h
• strlen()
• strcpy()
• strncpy()
• strcat()
• strncat()
• strcmp()
• strncmp()
• strchr()
• strstr()
• gets()
• puts()
• scanf()
• printf()
• fgets()
• fputs()
• Memory management
• Dynamic memory allocation
• malloc()
• calloc()
• realloc()
• Buffer overflow
• Escape sequences
• Null-termination
• Safe programming practices