Summary of common string processing functions in C language

1、char *strcat(char *s1, const char *s2)

Splicing string function , hold s2 Joining together to s1 After the string , The return value points to s1 The pointer to

int main()
{
	char s1[] = "aba";
	char s2[] = "cdf";
	printf(" Before splicing s1 length ：%d   s2 length : %d\n", strlen(s1), strlen(s2));
	char *s3=strcat(s1, s2);
	//s3 Equate to s1
	printf(" Print s1: %s\n", s1);
	printf(" Print s3: %s\n", s3);
	printf(" After splicing s1 length ：%d   s2 length : %d   s3 length ：%d\n", strlen(s1), strlen(s2),strlen(s3));
}

Be careful ：s2 Joining together to s1 Back ,s1 The length of will change from the original 3 Turn into 6（ No end character ）, Here the program does not report an error because C Language does not detect array subscript out of bounds , So it's using strcat() Function, try to give enough memory space , In addition to calculating the number of characters after splicing, you need to add 1 Just enough space to store the empty characters at the end . So at the beginning of the definition s1 When it comes to length, it is best to consider the length after splicing , The initial length here is set to ：s1 The length of +s2 The length of + Terminator =3+3+1=7, Although the program may not report an error after buffer overflow , But for the safety of the program, it's better to be rigorous .

2、char *strstr(const char *s1, const char *s2)

lookup s2 First appeared in s1 The location of , return s2 For the first time in s1 The first address that appears , Returns if none exists NULL

int main()
{
	//s2 stay s1 We can find 
	char s1[] = "acdrtcdrj";
	char s2[] = "cdr";
	char *s3 = strstr(s1, s2);
	printf("%s\n", s3);

	//str2 stay str1 Cannot be found in 
	char str1[] = "acdrtcdrj";
	char str2[] = "cdrx";
	char *str3 = strstr(str1, str2);
	printf("%s\n", str3);
}