strcat()、strcpy()、strcmp()、strlen()

const The value of the modified variable or object remains unchanged , Protect the contents of variables or objects from being modified during invocation

1、 String concatenation function strcat

The function prototype is strcat(char[],const char[])

The first 2 Declared as an array of characters const, To ensure that the contents of the array will not be modified during the function call

that , Why not put the second 1 An array of characters is also declared as const Well ？

In order to make 2 The contents of the first array overwrite the... At the end of the first array '\0', The sign of whether the string ends is '\0' The location of , If an array contains more than one '\0', You encounter the first '\0' When it's over

#include <iostream>
using namespace std;
int main() {
	char a[30]="i love ";// Make sure the array is long enough to accommodate two plus 
	char b[] = "china";
	cout << strcat(a, b)<< endl;
	return 0;
}

2、 String copy function strcpy

The function prototype strcpy(char[],const char[])

The first 2 An array of characters does not change , Will be the first 1 The corresponding characters in the character array are overwritten

#include <iostream>
using namespace std;
int main() {
	char a[100];
	char b[] = "i love china";
	strcpy(a, b);
	cout << a<< endl;
	return 0;
}

3、 String comparison function strcmp

The function prototype strcmp(const char[],const char[])

The purpose is to compare these two strings , Therefore, we should only compare and not change

The preceding string > String after , A positive number , Ahead < hinder , The value is negative. , Ahead = hinder , The value is 0

#include <iostream>
using namespace std;
int main() {
	char a[] = "i love china";
	char b[] = "i love";
	cout << strcmp(a,b) << endl;
	return 0;
}

4、 String length function strlen

The function prototype strlen(const chat[])

Actual length , barring '\0', Errors may be reported in the application ： Not added for string 0 Terminator , Just initialize the string , Such as char str[100]={0}

#include <iostream>
using namespace std;
int main() {
	char a[] = "i love china";
	cout << strlen(a) << endl;
	return 0;
}