如何在不使用动态内存分配的情况下将字符指针填充到另一个指针中

Question

我试图在结构内的另一个指针内分配一个字符指针。我的环境没有 malloc/calloc，因此动态内存分配不是一种选择。我如何才能在 read_string_from_byte_array() 函数中填充字符指针？

    typedef struct custom_string
    {
        char textt[5];
        int length;
    }custom_string;

    typedef struct custom_string_container
    {
        custom_string* string;
    }custom_string_container;

    void read_string_from_byte_array(custom_string_container* string_container)
    {
        char* byte_array = "12345";
        int i;

        puts("assigning");
        for(i = 0; i < 5; i++)
        {
            string_container->string->textt[i] = byte_array[i]; //failing with exit code 139
        }

        puts("done assigning");

    }



    void main()
    {
        //dynamic memory allocation is strictly prohibited
        custom_string_container string_container;

        read_string_from_byte_array(&string_container);
        printf("read string is %s \n", string_container.string->textt);

    }

Answer 1

如果您不想在堆中进行动态分配，请替换

typedef struct custom_string_container
{
    custom_string * string;
}custom_string_container;

通过

typedef struct custom_string_container
{
    custom_string string;
}custom_string_container;

当然在需要的时候用'.'替换'->'

还有警告

    for(i = 0; i < 5; i++)
    {
        string_container->string->textt[i] = byte_array[i]; //failing with exit code 139
    }

空终止字符丢失，这是做时的问题

printf("read string is %s \n", string_container.string->textt);

如果你想存储 5 个字符（不计算空字符） 在 for 之后添加 string_container->string->textt[i] = 0; 或将 i < 5 替换为 i <= 5 以同时复制空字符

当然在struct custom_string中用char textt[6];替换char textt[5];

注意在大小写 6 然后在其他地方写 5 或 6 是危险的，以防你改变大小，使用 sizeof 更安全

终于有了所有的变化：

typedef struct custom_string
{
    char textt[6];
    int length;
}custom_string;

typedef struct custom_string_container
{
    custom_string string;
}custom_string_container;

void read_string_from_byte_array(custom_string_container* string_container)
{
    char* byte_array = "12345";
    int i;

    puts("assigning");
    for(i = 0; i < sizeof(string_container->string.textt); i++)
    {
        string_container->string.textt[i] = byte_array[i]; 
    }
    string_container->string.textt[i] = 0;

    puts("done assigning");

}



void main()
{
    //dynamic memory allocation is strictly prohibited
    custom_string_container string_container;

    read_string_from_byte_array(&string_container);
    printf("read string is %s \n", string_container.string.textt);

}

执行：

assigning
done assigning
read string is 12345 

在 valgrind 下：

pi@raspberrypi:~ $ valgrind ./a.out 
==8507== Memcheck, a memory error detector
==8507== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==8507== Using Valgrind-3.13.0 and LibVEX; rerun with -h for copyright info
==8507== Command: ./a.out
==8507== 
assigning
done assigning
read string is 12345 
==8507== 
==8507== HEAP SUMMARY:
==8507==     in use at exit: 0 bytes in 0 blocks
==8507==   total heap usage: 1 allocs, 1 frees, 1,024 bytes allocated
==8507== 
==8507== All heap blocks were freed -- no leaks are possible
==8507== 
==8507== For counts of detected and suppressed errors, rerun with: -v
==8507== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 6 from 3)

---

还要注意，read_string_from_byte_array 中的复制可以简单地使用 strncpy 完成（如果 byte_array 太长而无法在 中记住，则不能使用 strcpy textt) 而不是 for 循环