c - Strlwr 函数 - 在 xcode 9.2 中出现错误

Question

我试图将字符串从大写转换为小写以检查它是否是回文，但是我不断收到错误:

“函数声明不是原型(prototype)”

我已经添加了#include <string.h>在标题中，但它仍然不起作用。我该如何解决这个问题？

这是代码:

int main (void)
{
    char *user_string, *user_string_rev;
    
    /* the malloc function is used to make sure that enough memory is allocated for the string and that it does not overwrite memory boxes of other variables. */
    user_string= (char*)malloc(BUFF_SIZE*sizeof(char));
    user_string_rev= (char*)malloc(BUFF_SIZE*sizeof(char));
    printf("Please enter a string:");
    fgets(user_string,BUFF_SIZE, stdin); /* fgets function take the string the user inputs and stores it into user_string. */
    user_string_rev=strcpy(user_string_rev, user_string); /*the strcpy takes the string the user inputs and copies it to user_string_rev. */
    strlwr(user_string_rev);
    
    palindrome_check(user_string,user_string_rev); /*this is the palindrome function used to check if the two strings are palindromes, it intakes two arguments, the two strings and does not return anything. */
    
    return 0;
    
}

Answer 1

替换:

strlwr(user_string_rev);

这不是一个标准函数:

int i = 0;
while (user_string_rev[i])
{
    if (isalpha(user_string_rev[i]))
        user_string_rev[i] |= 32;
    ++i;
}

不要忘记在 .c 文件顶部添加 ctype header 以使用 isalpha:

#include <ctype.h>