Created: 2023-01-15 17:57
Status: #concept
Subject: Programming
Tags: C C String Library Function stdio.h

string.h

Description

A C Standard Library containing essential C String Functions such as; assignment, length finding, concatenation, and comparison.

What does strcpy (String Copy) do? What's the syntax?

char *strcpy(char *str1, const char *str2);

The strcpy() function copies the string pointed by source str2 (including the null character) to the destination str1.
Think of it as: destination = source or str1 = str2.
It returns the copied string.

strncpy(str1, str2, sizeof(str1));

Copies str2 to str1 until sizeof(str1).
Safer and guarantees no characters to overlap inaccessible Memory Addresses.

What does strlen (String Length) do? What’s the syntax?

size_t strlen(const char *str);

It returns the length of a string str: up to, but not including the first '\0'.
C strlen Illustration.png

What does strcat (String Concatenation) do? What’s the syntax?

char *strcat(char *str1, const char *str2);

Appends the Characters of the source string str2 to the end of the destination string str1 starting from the Null Terminator \0, then adds another \0 at the end.
Returns a Pointer to the resulting string str1.

char *strncat(char *str1, const char *str2, size_t n);

What does strcmp (String Comparison) do? What’s the syntax?

int strcmp(const char *str1, const char *str2);

Compares str1 and str2, returning a value less than, equal to, or greater than 0, depending on lexicographic ordering of the elements of str1 and str2.

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

int main(void)
{
	char s1[50] = "Hello", s2[50] = "Hello";
	printf("%d", strcmp(s1, s2)); // outputs 0
	
	char s1[50] = "Hello", s2[50] = "Hello World";
	printf("%d", strcmp(s1, s2)); // outputs -1
	
	char s1[50] = "Hello World", s2[50] = "Hello";
	printf("%d", strcmp(s1, s2)); // outputs 1
}

References

C Programming, A Modern Approach, 2nd Edition, Chapter 13.5