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C String Functions


String Functions

C also has many useful string functions, which can be used to perform certain operations on strings.

To use them, you must include the <string.h> header file in your program:

#include <string.h>

String Length

For example, to get the length of a string, you can use the strlen() function:

Example

char alphabet[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
printf("%d", strlen(alphabet));
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In the Strings chapter, we used sizeof to get the size of a string/array. Note that sizeof and strlen behaves differently, as sizeof also includes the \0 character when counting:

Example

char alphabet[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
printf("%d", strlen(alphabet));   // 26
printf("%d", sizeof(alphabet));   // 27
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It is also important that you know that sizeof will always return the memory size (in bytes), and not the actual string length:

Example

char alphabet[50] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
printf("%d", strlen(alphabet));   // 26
printf("%d", sizeof(alphabet));   // 50
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Concatenate Strings

To concatenate (combine) two strings, you can use the strcat() function:

Example

char str1[20] = "Hello ";
char str2[] = "World!";

// Concatenate str2 to str1 (result is stored in str1)
strcat(str1, str2);

// Print str1
printf("%s", str1);
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Note that the size of str1 should be large enough to store the result of the two strings combined (20 in our example).


Copy Strings

To copy the value of one string to another, you can use the strcpy() function:

Example

char str1[20] = "Hello World!";
char str2[20];

// Copy str1 to str2
strcpy(str2, str1);

// Print str2
printf("%s", str2);
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Note that the size of str2 should be large enough to store the copied string (20 in our example).


Compare Strings

To compare two strings, you can use the strcmp() function.

It returns 0 if the two strings are equal, otherwise a value that is not 0:

Example

char str1[] = "Hello";
char str2[] = "Hello";
char str3[] = "Hi";

// Compare str1 and str2, and print the result
printf("%d\n", strcmp(str1, str2));  // Returns 0 (the strings are equal)

// Compare str1 and str3, and print the result
printf("%d\n", strcmp(str1, str3));  // Returns -4 (the strings are not equal)
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