用户输入的结果不稳定。

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英文:

C user input sporadic invalid results

问题

在使用C语言编码时,我遇到了用户输入的问题。有时候输入有效,有时候无效。

从终端输出的示例运行结果来看:

dennis@MBP2021 Encryption % make
cc Gronsfeld_Cipher.c /Users/dennis/Documents/C/programs/DJSlibrary/cs50.c -o cipher
dennis@MBP2021 Encryption % ./cipher 

Please enter line to be encoded: This, however, is not the time.

You entered: This, however, is not the time. Length: 31

The message is:  This, however, is not the time.
The cipher is:   EZNH, SCVKOHZ, KF UFP GXF ONWX.
The decipher is: THIS, HOWEVER, IS NOT THE TIME.


dennis@MBP2021 Encryption % ./cipher

Please enter line to be encoded: This, however, is not the time, nor the place to have fun.

You entered: This, however, is not the time, nor the place to have fun. Length: 58
zsh: trace trap  ./cipher
dennis@MBP2021 Encryption % 

代码片段:

char data[] = "Dummy";
int keys[] = {11, 7, 13, 10, 25, 9, 8, 3};  


// Do the stuff
int main(void)
{   
    // Get input from user
    char *string_input = NULL;
    size_t string_size = 250;
    ssize_t bytes_read;

    printf("\nPlease enter line to be encoded: ");
    string_input = (char *) malloc(string_size);
    bytes_read = getline(&string_input, &string_size, stdin);

    if(bytes_read < 2)
    {
        printf("\n\nNo input was entered. Program terminating.\n");
        printf("Error Code: 1\n\n");
        free(string_input);
        return 1; 
    }

    string_input[bytes_read-1] = 0; // Clear out the new line.
    
    printf("\nYou entered: %s Length: %ld\n", string_input, bytes_read-1);
    strcpy(data, string_input);
    free(string_input);

    // Get sizes
    int DataLen = strlen(data);
    int ks = sizeof(keys) / sizeof(keys[0]);

    printf("\nThe message is:  %s", data);

根据我在终端上看到的情况,它在strcpy处崩溃(我猜测)。代码中的这一行 string_input[bytes_read-1] = 0; // Clear out the new line 试图删除字符串输入末尾的换行符。它从未执行到最后一个printf语句。我不明白为什么它可以处理一个较短的行(31个字节),而不能处理58个字节的行。我尝试在VSCode中使用调试功能,但它不允许我输入一行输入。我还需要找出其他原因。另外,我是C编程的新手。提前感谢您的帮助。

英文:

Coding in C, I'm having an issue with user input. Sometimes, the input works and sometimes it doesn't.

Example run output from terminal:

dennis@MBP2021 Encryption % make
cc Gronsfeld_Cipher.c /Users/dennis/Documents/C/programs/DJSlibrary/cs50.c -o cipher
dennis@MBP2021 Encryption % ./cipher 

Please enter line to be encoded: This, however, is not the time.

You entered: This, however, is not the time. Length: 31

The message is:  This, however, is not the time.
The cipher is:   EZNH, SCVKOHZ, KF UFP GXF ONWX.
The decipher is: THIS, HOWEVER, IS NOT THE TIME.


dennis@MBP2021 Encryption % ./cipher

Please enter line to be encoded: This, however, is not the time, nor the place to have fun.

You entered: This, however, is not the time, nor the place to have fun. Length: 58
zsh: trace trap  ./cipher
dennis@MBP2021 Encryption % 

code snippet:

char data[] = &quot;Dummy&quot;;
int keys[] = {11, 7, 13, 10, 25, 9, 8, 3};  


// Do the stuff
int main(void)
{   
    // Get input from user
    char *string_input = NULL;
    size_t string_size = 250;
    ssize_t bytes_read;

    printf(&quot;\nPlease enter line to be encoded: &quot;);
    string_input = (char *) malloc(string_size);
    bytes_read = getline(&amp;string_input, &amp;string_size, stdin);

    if(bytes_read &lt; 2)
    {
        printf(&quot;\n\nNo input was entered. Program terminating.\n&quot;);
        printf(&quot;Error Code: 1\n\n&quot;);
        free(string_input);
        return 1; 
    }

    string_input[bytes_read-1] = 0; // Clear out the new line.
    
    printf(&quot;\nYou entered: %s Length: %ld\n&quot;, string_input, bytes_read-1);
    strcpy(data, string_input);
    free(string_input);

    // Get sizes
    int DataLen = strlen(data);
    int ks = sizeof(keys) / sizeof(keys[0]);

    printf(&quot;\nThe message is:  %s&quot;, data);

According to what I see on the terminal, it dies at the strcpy (I guess) The line string_input[bytes_read-1] = 0; // Clear out the new line is trying to remove the line feed at the end of the string input. It never gets to the last printf. I don't understand why it worked with a small line (31 bytes) and not the 58 byte line. I tried to use debug in vscode, but it doesn't allow me to enter an input line. Something else I need to find out. Also, I'm new to C programming. Thanks in advance.

答案1

得分: 1

问题很可能出在这个语句上:

strcpy(data, string_input);

在这里,你将数据复制到一个只能容纳六个字符(包括空字符)的数组中。

当你创建和初始化data数组时,只为字符串"Dummy"分配了空间,没有更多的空间。

如果输入的长度超过五个字符,那么就会越界访问data,导致未定义行为

data数组设置一个特定的大小,足够容纳最大的输入。

或者继续使用string_input,根本不使用data

英文:

The problem is very likely this statement:

strcpy(data, string_input);

Here you copy data into an array that can only hold six characters, null-terminator included.

When you create and initialize the data array you only make space for the string &quot;Dummy&quot;, nothing more.

If the input it longer than five characters, then that means you will write out of bounds of data, and have undefined behavior.

Set a specific size for the data array, one that is big enough to hold the largest input.

Or keep on using string_input, and don't use data at all.

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  • 本文由 发表于 2023年8月9日 00:12:32
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