Question

所以我要做的这个课程要我们玩内存管理和指针。我并没有完全理解它们。

我一直收到错误：

分段错误（核心转储）

显然我无法访问记忆？

我的slen函数出了什么问题？

/*

In these exercises, you will need to write a series of C functions. Where possible, these functions should be reusable (not use global variables or fixed sized buffers) and robust (they should not behave badly under bad input eg empty, null pointers) .
As well as writing the functions themselves, you must write small programs to test those functions.

- Remember, in C, strings are sequences of characters stored in arrays AND the character sequence is delimited with '\0' (character value 0).

----------------------------------------------------

1) int slen(const char* str)
    which returns the length of string str [slen must not call strlen - directly or indirectly]
*/

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

/* Returns the length of a given string */
int slen(const char* str) {
    int size = 0;
    while(str[size] != '\0') {
        size++;
    }
    return size;
}

/*
2) char* copystring(const char* str)
    which returns a copy of the string str. [copystring must not call any variant of strcpy or strdup - directly or indirectly]*/
char* copystring(const char* str) {
    int size = slen(str);
    char *copy = (char*) malloc (sizeof(char) * (size + 1));
    copy[size] = '\0';
    printf("before loop");
    int i = 0;
    while (*str != '0') {
        copy[i++] = *str++;
    }
    return copy;
}


int main() {
    char *msg = NULL;
    printf("Enter a string: ");
    scanf("%s", &msg);
    int size = slen(msg);
    //printf("The length of this message is %d.", size);
//  printf("Duplicate is %s.", copystring(msg));

    // Reading from file


}

Answer 1

问题不在您的slen功能中，在您使用scanf之前就已经发生了：

您需要为使用scanf
您不需要将内存缓冲区的地址传递给scanf，该变量已经存有地址。

修改后的代码：

char msg[101];
printf("Enter a string: ");
scanf("%s", msg);
int size = slen(msg);

或者，如果您被要求了解内存分配，请研究malloc的使用情况：

char *msg = malloc(101);
printf("Enter a string: ");
scanf("%s", msg);
int size = slen(msg);

在了解malloc时，不要忘记研究free的相关用法。

此处重要且重要的是管理缓冲区大小：当您为用户扫描的字符串创建内存时，您应该限制实际读。有几种方法可以做到这一点：首先研究scanf格式字符串，您可以在其中使用：

scanf("%100s", msg);

Answer 2

您需要为msg中的main分配内存使用char msg[10]或使用malloc。 char *msg = malloc(10*sizeof(char))

C语言的初学者：字符串和内存

2 个答案: