C language: string processing function

String concatenation function strcat()

strcat yes string catenate Abbreviation , It means splicing two strings together , The grammar format is ：

strcat(arrayName1, arrayName2);

arrayName1、arrayName2 For the string to be spliced .

strcat() Will put arrayName2 Connect to arrayName1 Back , And delete the original arrayName1 The last end sign '\0'. It means ,arrayName1 It has to be long enough , Be able to accommodate arrayName1 and arrayName2, Otherwise you cross the line （ Out of range ）.

strcat() The return value of is arrayName1 The address of . 

The reference sample ：

#include <stdio.h>
#include<string.h> 
int main(){
    char str[20] = "http:";
    char str1[20]="//csdn.com";
    strcat(str,str1);
    puts(str);
    return 0;
}

Reference results ：

  String copy function strcpy()

strcpy yes string copy Abbreviation , It means string copy , That is, the string is copied from one place to another , The grammar format is ：

strcpy(arrayName1, arrayName2);

strcpy() Will be able to arrayName2 Copy the string in to arrayName1 in , String end flag '\0' Also copy together . Please see the following example ： 

The reference sample ：

#include <stdio.h>
#include<string.h> 
int main(){
    char str[20] = "hello world!";
    char str1[20]="HELLO WORLD!";
    strcpy(str,str1);
    puts(str);
    return 0;
}

Reference results ：

You see , take str2 Copied to the str1 after ,str1 The content from the Central Plains is covered .

in addition ,strcpy() requirement arrayName1 Have enough length , Otherwise, you cannot load all the copied strings .

String comparison function strcmp() 

strcmp yes string compare Abbreviation , It means string comparison , The grammar format is ：

strcmp(arrayName1, arrayName2);

arrayName1 and arrayName2 Are two strings that need to be compared .

The character itself has no size ,strcmp() ... corresponding to each character ASCII Code value for comparison .strcmp() From the second... Of the two strings 0 Characters start to compare , If they are equal , Just continue to compare the next character , Until you meet different characters , Or to the end of the string .

Return value ： if arrayName1 and arrayName2 identical , Then return to 0; if arrayName1 Greater than arrayName2, Return greater than 0 Value ; if arrayName1 Less than arrayName2, Then return less than 0 Value .

The reference sample ：

#include <stdio.h>
#include <string.h>
int main(){
    char a[] = "aBcDeF";
    char b[] = "AbCdEf";
    char c[] = "aacdef";
    char d[] = "aBcDeF";
    printf("a VS b: %d\n", strcmp(a, b));
    printf("a VS c: %d\n", strcmp(a, c));
    printf("a VS d: %d\n", strcmp(a, d));
   
    return 0;
}

  Reference results ：

Get string length function strlen()

strlen yes string length Abbreviation , It means string length , The grammar is ：

strlen(string) 

The reference sample ：

#include <stdio.h>
#include <string.h>
int main(){
    char a[] = "aBcDeF";
    int len=strlen(a);
    printf("%d",len);
    return 0;
}

Reference results ：

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