C language function strcmp() (compare two strings)

C Library function - strcmp()

describe

C Library function int strcmp(const char *str1, const char *str2) hold str1 The string pointed to and str2 Compare the string pointed to .

Statement

Here is strcmp() Declaration of functions .

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

Parameters

• str1 – The first string to compare .
• str2 – The second string to compare .

Return value

The return value of this function is as follows ：

• If the return value is less than 0, said str1 Less than str2.
• If the return value is greater than 0, said str1 Greater than str2.
• If the return value is equal to 0, said str1 be equal to str2.

example

The following example demonstrates strcmp() Function usage .

#include <stdio.h>
#include <stdlib.h>

int main()
{ 
    
    char str1[15];
    char str2[15];
    int ret;


    strcpy(str1, "abcdef");
    strcpy(str2, "ABCDEF");

    ret = strcmp(str1, str2);

    if (ret < 0)
    { 
    
        printf("str1  Less than  str2");
    }
    else if (ret > 0)
    { 
    
        printf("str1  Greater than  str2"); //str1  Greater than  str2
    }
    else
    { 
    
        printf("str1  be equal to  str2");
    }

    return(0);
}

Be careful

Two strings are compared character by character from left to right （ Press ASCII Compare the value with the size ）, Until a different character appears or \0 until . Such as ：

1. “A”<“B”
2. “A”<“AB”
3. “Apple”<“Banana”
4. “A”<“a”
5. “compare”<“computer”

Particular attention ：strcmp(const char *s1,const char * s2) You can only compare strings , Can be used to compare two string constants , Or compare array and string constants , You can't compare other forms of parameters such as numbers .

ANSI The standard stipulates , The return value is a positive number , negative ,0 . And the exact value depends on different C Realized .

When two strings are not equal ,C The standard does not specify that the return value will be 1 or -1, Only positive and negative numbers are specified .

Some will put two characters ASCII The difference of codes is returned by the function value as the comparison result . But in any case, this basis can not be used as the process logic in the program .

Reference article ：C Library function - strcmp()