使用 scanf() 函数 [英] Using the scanf() function

问题描述

我打算修改一个特定字符串的每个其他字母.但就本程序而言，这些都不会发生.到目前为止，我已经从用户那里获取了一个字符串并将其存储在 userinput 中并打算打印它.

I intend to modify each other letter of a particular string. But for the purposes of this program none of that occurs. So far I've grabbed a string from the user and stored it in userinput and intend to print it.

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

int main(void) {    
char userinput[256] ="";
printf("Enter somthing to change:\n");
scanf("%s", &userinput);
printf("%s\n", userinput);

int k = 2; // This is just here to do something every time k is even
int j = strlen(userinput);
for (int i = 0; i < j; i++) {

    if(k % 2 == 0) {
        printf("%s", userinput[i]);
        k++;
    }
    else {
        printf("%s", userinput[i]);
        k++;
    }
}

}

strlen() 函数在 userinput 上不起作用.我认为这是因为 strlen() 应该取字符串的第一个字符的地址，然后迭代直到到达一个空字符，但 scanf 实际上并没有创建一个空字符.在不知道字符串长度的情况下，我想不出在字符串后面添加 '\0' 的方法.

The strlen() function however does not work on the userinput. I figure this is because strlen() is supposed to take the address of the first char of a string and then iterate until reaching a null char but scanf doesn't actually create a null char. I couldn't figure out a way of adding the '\0' after the string without first knowing the length of the string.

如果存储在数组中，我将如何访问存储字符序列的长度?

How would I go about accessing the length of a stored character sequence if it's stored in an array?

推荐答案

这个:

scanf("%s", &userinput);

应该是:

scanf("%s", userinput);

操作员 & 的地址是不需要的，并且不正确.当传递给函数时，数组衰减到它们的第一个元素的地址.scanf("%s") 将附加一个空终止字符，因此没有必要显式插入一个.

The address of operator & is unrequired, and incorrect. Arrays decay to the address of their first element when passed to a function. scanf("%s") will append a null terminating character so it is unnecessary to explicitly insert one.

为了防止潜在的缓冲区溢出，指定scanf() 应该写入userinput 的最大字符数.这应该比 userinput 的大小小 1，为终止空字符留出空间:

To prevent potential buffer overrun specify the maximum number of characters that scanf() should write to userinput. This should be one less than the size of userinput, leaving room for the terminating null character:

scanf("%255s", userinput);

不正确的格式说明符(这是未定义的行为)被用于打印 userinput 的 characters: use %c not <代码>%s.这:

The incorrect format specifier (which is undefined behaviour) is being used to print the characters of userinput: use %c not %s. This:

printf("%s", userinput[i]);

必须是:

printf("%c", userinput[i]);

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