Welcome to the topic of String Manipulation in C language! This topic is crucial as it equips you with the skills to work with text data, a common and essential aspect of programming. By the end of this lesson, you'll be able to create, modify, compare, search, and manipulate strings efficiently.
Strings in C are arrays of characters terminated by a null character \0. String literals are enclosed within double quotes ("). Let's explore some key terms:
strlen(string).substring[start:end].strcat(destination, source) function or the addition operator (+).#include <stdio.h>
#include <string.h>
int main() {
char string1[20] = "Hello";
char string2[20] = "World";
char combined[40];
// Concatenation with strcat()
strcat(combined, string1);
strcat(combined, " ");
strcat(combined, string2);
printf("Combined: %s\n", combined);
// Concatenation with addition operator
char concat[40];
concat[0] = string1[0];
concat[1] = ' ';
int i;
for (i = 0; string2[i] != '\0'; ++i) {
concat[i + 1] = string2[i];
}
concat[i + 1] = '\0';
printf("Combined (with addition operator): %s\n", concat);
return 0;
}
In this example, we combine two strings using strcat() and the addition operator. The output will be:
Combined: Hello World
Combined (with addition operator): Hello World
What causes it: Writing more characters to a string than its allocated buffer size.
#include <stdio.h>
int main() {
char str[5] = "Hello";
// Adding one extra character causes a buffer overflow error
strcat(str, " World");
}
Error message:
Segmentation fault (core dumped)
Solution: Ensure that you allocate sufficient space for your string and avoid writing beyond the buffer's limit.
Why it happens: The program tries to write more characters than the allocated buffer can hold, causing memory corruption and a segmentation fault.
How to prevent it: Allocate enough memory for your strings or dynamically resize them when necessary using functions like realloc().
What causes it: Failing to include a null character at the end of a string.
#include <stdio.h>
int main() {
char str[5] = "Hello";
// Forgetting the null character makes it a string literal instead of a character array
printf("%s\n", str);
}
Error message: None in this example because it's a syntax error, not a runtime error.
Solution: Always end your strings with a null character ('\0').
Why it happens: Leaving out the null character makes it impossible for the program to determine the string's length and causes issues when using functions that rely on the null character, such as strlen().
How to prevent it: Be mindful of adding a null character at the end of your strings. You can use the sprintf() function with a format string like "%s\0" to ensure the last character is always a null character.
What causes it: Comparing strings lexicographically instead of comparing their addresses in memory.
#include <stdio.h>
int main() {
char str1[5] = "Hello";
char str2[5] = "Hello";
printf("%d\n", str1 == str2); // Outputs: 1 (true) due to comparison by address, not lexicography
}
Error message: None in this example because it's a logic error.
Solution: Use strcmp() or strcasecmp() to compare strings lexicographically instead of comparing their addresses in memory.
Why it happens: Comparing strings using the == operator compares their addresses, not their contents. The two strings might be located at different memory addresses even if they have identical content.
How to prevent it: Use functions like strcmp() or strcasecmp() to compare strings based on their lexicographical order.
malloc().strcpy(), as it does not include a null character at the end of the destination string by default. Consider using strncpy(destination, source, size) to ensure the destination array is properly terminated.strlen() to check the length of strings before performing operations, especially when dealing with user input or dynamically allocated memory.Next steps for learning include exploring more advanced topics like regular expressions and searching algorithms for strings. Happy coding!