如何正确地比较字符串?

I am trying to get a program to let a user enter a word or character, store it, and then print it until the user types it again, exiting the program. My code looks like this:

我正在尝试获得一个程序，让用户输入一个字或字符，存储它，然后打印它，直到用户再次输入它，退出程序。我的代码是这样的:

#include <stdio.h>

int main()
{
    char input[40];
    char check[40];
    int i=0;
    printf("Hello!\nPlease enter a word or character:\n");
    gets(input);
    printf("I will now repeat this until you type it back to me.\n");

    while (check != input)
    {
        printf("%s\n", input);
        gets(check); 
    }

    printf("Good bye!");


    return 0;
}

The problem is that I keep getting the printing of the input string, even when the input by the user (check) matches the original (input). Am I comparing the two incorrectly?

问题是，即使用户输入(检查)与原始(输入)匹配，我仍然得到输入字符串的打印。我是不是把这两者比较错了?

7 个解决方案

#1

210

You can't (usefully) compare strings using != or ==, you need to use strcmp:

您不能(有效地)使用!=或==来比较字符串，您需要使用strcmp:

while (strcmp(check,input) != 0)

The reason for this is because != and == will only compare the base addresses of those strings. Not the contents of the strings themselves.

这样做的原因是!=和=将只比较这些字符串的基本地址。不是弦本身的内容。

#2

Ok a few things: gets is unsafe and should be replaced with fgets(input, sizeof(input), stdin) so that you don't get a buffer overflow.

好，有几件事:get是不安全的，应该用fgets(input, sizeof(input)， stdin)替换，这样就不会出现缓冲区溢出。

Next, to compare strings, you must use strcmp, where a return value of 0 indicates that the two strings match. Using the equality operators (ie. !=) compares the address of the two strings, as opposed to the individual chars inside them.

接下来，要比较字符串，必须使用strcmp，其中返回值为0表示两个字符串匹配。使用等式运算符。比较两个字符串的地址，而不是它们内部的字符。

And also note that, while in this example it won't cause a problem, fgets stores the newline character, '\n' in the buffers also; gets() does not. If you compared the user input from fgets() to a string literal such as "abc" it would never match (unless the buffer was too small so that the '\n' wouldn't fit in it).

还要注意，虽然在本例中它不会引起问题，但fgets也会在缓冲区中存储换行字符‘\n’;()不。如果您将来自fgets()的用户输入与字符串文本(如“abc”)进行比较，那么它将永远不会匹配(除非缓冲区太小，以至于‘\n’无法容纳它)。

EDIT: and beaten by the super fast Mysticial once again.

编辑:又一次被超快神秘术打败。

#3

You can't compare arrays directly like this

不能像这样直接比较数组

array1==array2

You should compare them char-by-char; for this you can use a function and return a boolean (True:1, False:0) value. Then you can use it in the test condition of the while loop.

你应该对它们逐个进行比较;为此，您可以使用一个函数并返回一个布尔值(True:1, False:0)。然后您可以在while循环的测试条件中使用它。

Try this:

试试这个:

#include <stdio.h>
int checker(char input[],char check[]);
int main()
{
    char input[40];
    char check[40];
    int i=0;
    printf("Hello!\nPlease enter a word or character:\n");
    scanf("%s",input);
    printf("I will now repeat this until you type it back to me.\n");
    scanf("%s",check);

    while (!checker(input,check))
    {
        printf("%s\n", input);
        scanf("%s",check);
    }

    printf("Good bye!");

    return 0;
}

int checker(char input[],char check[])
{
    int i,result=1;
    for(i=0; input[i]!='\0' || check[i]!='\0'; i++) {
        if(input[i] != check[i]) {
            result=0;
            break;
        }
    }
    return result;
}

#4

Use strcmp.

使用比较字符串。

This is in string.h library, and is very popular. strcmp return 0 if the strings are equal. See this for an better explanation of what strcmp returns.

这是在字符串。h图书馆，很受欢迎。如果字符串相等，则strcmp返回0。有关strcmp返回的内容的更好解释，请参阅本文。

Basically, you have to do:

基本上，你必须这样做:

while (strcmp(check,input) != 0)

或

while (!strcmp(check,input))

或

while (strcmp(check,input))

You can check this, a tutorial on strcmp.

您可以查看这篇关于strcmp的教程。

#5

Whenever you are trying to compare the strings, compare them with respect to each character. For this you can use built in string function called strcmp(input1,input2); and you should use the header file called #include<string.h>

当您试图比较字符串时，请将它们与每个字符进行比较。为此，可以使用名为strcmp的字符串函数(input1,input2);您应该使用名为#include的头文件

Try this code:

试试这段代码:

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

int main() 
{ 
    char s[]="*";
    char s1[200];
    printf("Enter the string to be checked\n");//enter the input string
    scanf("%s",s1);
    if(strcmp(s,s1)==0)//compare both the strings  
    {
        printf("Both the Strings match\n"); 
    } 
    else
    {
        printf("Entered String does not match\n");  
    } 
    system("pause");  
}

#6

Unfortunately you can't use strcmp from <cstring> because it is a C++ header and you specifically said it is for a C application. I had the same problem, so I had to write my own function that implements strcmp:

不幸的是，您不能使用中的strcmp，因为它是一个c++头，而且您特别提到它是针对一个C应用程序的。我也有同样的问题，所以我必须编写自己的函数来实现strcmp:

int strcmp(char input[], char check[])
{
    for (int i = 0;; i++)
    {
        if (input[i] == '\0' && check[i] == '\0')
        {
            break;
        }
        else if (input[i] == '\0' && check[i] != '\0')
        {
            return 1;
        }
        else if (input[i] != '\0' && check[i] == '\0')
        {
            return -1;
        }
        else if (input[i] > check[i])
        {
            return 1;
        }
        else if (input[i] < check[i])
        {
            return -1;
        }
        else
        {
            // characters are the same - continue and check next
        }
    }
    return 0;
}

I hope this serves you well.

我希望这对你有好处。

#7

    #include<stdio.h>
    #include<string.h>
    int main()
    {
        char s1[50],s2[50];
        printf("Enter the character of strings: ");
        gets(s1);
        printf("\nEnter different character of string to repeat: \n");
        while(strcmp(s1,s2))
        {
            printf("%s\n",s1);
            gets(s2);
        }
        return 0;
    }

This is very simple solution in which you will get your output as you want.

这是一个非常简单的解决方案，您可以在其中得到您想要的输出。

#1

210