为任意长度的字符串动态分配内存

Question

我想创建一个函数来计算字符串str中字符c的出现次数，无论字符串c中的字符c是否为小写。我正在尝试使用toupper和tolower函数，但是它不起作用。

在主函数中，我想使用malloc函数为最多50个字符的字符数组动态分配内存，然后使用fgets读取输入字符串。然后，我想通过使用malloc函数但根据输入字符串的长度为输入字符串正确分配内存。然后，我想将输入字符串复制到正确大小的另一个字符串中，并释放开头分配的内存。我不知道为什么，但是malloc函数没有在一开始分配50个字符。当我打印输入字符串的长度时，它不算超过7个字符。我想念什么？

这是我的代码如下：

int count_insensitive(char *str, char c){
    int count = 0;
    for(int i = 0; str[i] != '\n'; i++){
        if(( str[i] == toupper(c)) || str[i] == tolower(c) ){
            count++;
        }     
    }
    return count;
}

int main(){
    char *a_str;
    a_str = (char *) malloc(sizeof(char) * 50);
    fgets(a_str, sizeof(a_str), stdin);
    printf("%lu\n", strlen(a_str));
    char *a_str2;
    a_str2 = (char *) malloc(sizeof(char) * (strlen(a_str)));
    strcpy(a_str2, a_str); 
    printf("%s\n", a_str2);
    free(a_str);

    printf("The character 'b' occurs %d times\n", count_insensitive(a_str2, 'b'));
    printf("The character 'H' occurs %d times\n", count_insensitive(a_str2, 'H'));
    printf("The character '8' occurs %d times\n", count_insensitive(a_str2, '8'));
    printf("The character 'u' occurs %d times\n", count_insensitive(a_str2, 'u'));
    printf("The character '$' occurs %d times\n", count_insensitive(a_str2, '$'));

如果输入此字符串：

Hello world hello world 

输出是这个：

7
hello w
The character 'b' occurs 15 times
The character 'H' occurs 47 times
The character '8' occurs 18 times
The character 'u' occurs 17 times
The character '$' occurs 6 times

Answer 1

通过执行chux注释和一些小的更改，这是代码的有效版本。我将在接下来的几个小时内写一些解释。

代码

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

int count_insensitive(char *str, char c){
    int count = 0;
    for(int i = 0; str[i] != '\n'; i++){
        if(( str[i] == toupper(c)) || str[i] == tolower(c) ){
            count++;
        }     
    }
    return count;
}


int main()
{

    char *a_str;
    a_str = malloc(50);
    fgets(a_str, 50, stdin);
    printf("%zu\n", strlen(a_str));
    char *a_str2;
    a_str2 = malloc(strlen(a_str));
    strcpy(a_str2, a_str); 
    printf("%s\n", a_str2);
    free(a_str);

    printf("The character 'b' occurs %d times\n", count_insensitive(a_str2, 'b'));
    printf("The character 'H' occurs %d times\n", count_insensitive(a_str2, 'H'));
    printf("The character '8' occurs %d times\n", count_insensitive(a_str2, '8'));
    printf("The character 'u' occurs %d times\n", count_insensitive(a_str2, 'u'));
    printf("The character '$' occurs %d times\n", count_insensitive(a_str2, '$'));

}