为什么 malloc 不接受全文？

Question

为什么当我尝试在变量 is 中输入文本时，它没有存储在完整的句子中。 malloc 似乎没有为字符串分配足够的内存，为什么？

所以对于 'second' 变量，当我输入 'is not happy why' 但是 'second' 仅存储 'is no' 时应该有足够的 space 用于字符串，为什么？

当我尝试下面的代码时：

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

/* Function Declerations */
char *str;
char *second;

/* Global Variables */

int main(){
    /* Initializing Global Variables */

    /* EXPERIMENTING WITH FGETS */
    /* Initial memory allocation */
    str = malloc(5 * sizeof(char));
    second = malloc(200 * sizeof(char));
    /* Get user input and print results */
    printf("Enter a string: "); // ask user to put in a string
    fgets(str, sizeof(str), stdin);
    str[strlen(str) - 1] = '[=10=]'; // Removes new line character of fgets
    printf("Enter a another string: "); // ask ujason is a godser to put in a string
    fgets(second, sizeof(second), stdin);
    second[strlen(second) - 1] = '[=10=]'; // Removes new line character of fgets
    printf("String = %s, Address of String is = %p\n", str, str);
    printf("String = %s, Address of String is = %p\n\n\n", second, second);

    
    /* Reallocating memory */
    str = (char *)realloc(str, (100 * sizeof(char)));
    printf("Combine text\n");
    strcat(str, second);
    printf("String = %s, Address of String is = %p\n", str, str);
    printf("String = %s, Address of String is = %p\n\n\n", second, second);

    free(str);
    free(second);
    return 0;
}

/* Function Details */

输出是：

Enter a string: jason
Enter a another string:  is not happy why
String = jason, Address of String is = 00000000001C2460
String =  is no, Address of String is = 00000000001C5FD0


Combine text
String = jason is no, Address of String is = 00000000001C70B0
String =  is no, Address of String is = 00000000001C5FD0

Answer 1

好的，所以当您调用 fgets 时，您传递了指针的大小。不是它指向的大小。

因此，例如，现在它正在运行：

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

/* Function Declerations */
char *str;
char *second;

/* Global Variables */

int main(){
    /* Initializing Global Variables */

    /* EXPERIMENTING WITH FGETS */
    /* Initial memory allocation */
    str = (char*) malloc(7 * sizeof(char));
    second =  (char*) malloc(200 * sizeof(char));
    /* Get user input and print results */
    printf("Enter a string: "); // ask user to put in a string
    fgets(str, 7, stdin);
    str[strlen(str)] = '[=10=]'; // Removes new line character of fgets
    printf("Enter a another string: "); // ask ujason is a godser to put in a string
    fgets(second, 200, stdin);
    second[strlen(second)] = '[=10=]'; // Removes new line character of fgets
    printf("\nString = %s, Address of String is = %p\n", str, str);
    printf("String = %s, Address of String is = %p\n\n\n", second, second);

    
    /* Reallocating memory */
    str = (char *)realloc(str, (100 * sizeof(char)));
    printf("Combine text\n");
    strcat(str, second);
    printf("String = %s, Address of String is = %p\n", str, str);
    printf("String = %s, Address of String is = %p\n\n\n", second, second);

    free(str);
    free(second);
    return 0;
}

您需要将实际大小而不是指针的大小传递给 fgets :)

为什么 malloc 不接受全文？

why does malloc not taking in the full text?

c

malloc

fgets

realloc