如何修复C语言结构体中strcpy引发的栈溢出及参数类型错误？

问题现象 #

运行包含日期与穿搭结构体的C程序，日期功能正常，但穿搭部分出现栈溢出错误，尝试添加/移除&符号后仍无法解决。

初始错误信息 #

main.c: In function ‘main’:
main.c:41:5: warning: ‘__builtin_memcpy’ writing 21 bytes into a region of size 0 overflows the destination [-Wstringop-overflow=]
   41 |     strcpy(&wtywtd.Face[100], "Prescription_Glasses");
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
main.c:34:19: note: at offset 500 into destination object ‘wtywtd’ of size 500
   34 |     struct Outfit wtywtd;
      |                   ^~~~~~
Todays date is 5/7/2016
*** stack smashing detected ***: terminated

初始代码 #

//Reviewing structures
#include <stdio.h>
#include <string.h>

int main()
{
    //The following is a structure for a date.
    //A structure can be defined as a group of variables
    
    struct date //Here, a structure called 'data', along with inner variable like the month, the date, and the year are displayed
    {
        int month;
        int day;
        int year;
    };
    
    //A variable must be declared to link the structure:
    struct date DateToday;
    
    //The following below shows how to assign values to inside the structure:
    DateToday.month = 5;
    DateToday.day = 7;
    DateToday.year = 2016;
    
    struct Outfit
    {
        char Footwear[100];
        char Bottoms[100];
        char Tops[100];
        char OverTop[100];
        char Face[100];
    };
    
    struct Outfit wtywtd;
    
    //When declaring strings, you must use double quotes
    strcpy(&wtywtd.Footwear[100], "Dark_Black_and_Gray_Nike_shoes");
    strcpy(&wtywtd.Bottoms[100], "Dark_Beige_Cargo_Shorts");
    strcpy(&wtywtd.Tops[100], "Dark_Red_And_Black_Striped_Tshirt");
    strcpy(&wtywtd.OverTop[100], "Grey_Hooded_Fleece_Jacket");
    strcpy(&wtywtd.Face[100], "Prescription_Glasses");
    
    printf("Todays date is %i/%i/%i", DateToday.month,DateToday.day,DateToday.year);
    printf("\nThe clothes I wore when going out were %s, %s, %s, %s, and %s", wtywtd.Footwear, wtywtd.Bottoms, wtywtd.Tops, wtywtd.OverTop, wtywtd.Face);
    
    return 0;
}

移除&后的错误信息 #

main.c: In function ‘main’:
main.c:37:27: warning: passing argument 1 of ‘strcpy’ makes pointer from integer without a cast [-Wint-conversion]
   37 |     strcpy(wtywtd.Footwear[100], "Dark_Black_and_Gray_Nike_shoes");
      |            ~~~~~~~~~~~~~~~^~~~~
      |                           |
      |                           char
In file included from main.c:3:
/usr/include/string.h:141:39: note: expected ‘char * restrict’ but argument is of type ‘char’
  141 | extern char *strcpy (char *__restrict __dest, const char *__restrict __src)
      |                      ~~~~~~~~~~~~~~~~~^~~~~~
main.c:38:26: warning: passing argument 1 of ‘strcpy’ makes pointer from integer without a cast [-Wint-conversion]
   38 |     strcpy(wtywtd.Bottoms[100], "Dark_Beige_Cargo_Shorts");
      |            ~~~~~~~~~~~~~~^~~~~
      |                          |
      |                          char
In file included from main.c:3:
/usr/include/string.h:141:39: note: expected ‘char * restrict’ but argument is of type ‘char’
  141 | extern char *strcpy (char *__restrict __dest, const char *__restrict __src)
      |                      ~~~~~~~~~~~~~~~~~^~~~~~
main.c:39:23: warning: passing argument 1 of ‘strcpy’ makes pointer from integer without a cast [-Wint-conversion]
   39 |     strcpy(wtywtd.Tops[100], "Dark_Red_And_Black_Striped_Tshirt");
      |            ~~~~~~~~~~~^~~~~
      |                       |
      |                       char
In file included from main.c:3:
/usr/include/string.h:141:39: note: expected ‘char * restrict’ but argument is of type ‘char’
  141 | extern char *strcpy (char *__restrict __dest, const char *__restrict __src)
      |                      ~~~~~~~~~~~~~~~~~^~~~~~
main.c:40:26: warning: passing argument 1 of ‘strcpy’ makes pointer from integer without a cast [-Wint-conversion]
   40 |     strcpy(wtywtd.OverTop[100], "Grey_Hooded_Fleece_Jacket");
      |            ~~~~~~~~~~~~~~^~~~~
      |                          |
      |                          char
In file included from main.c:3:
/usr/include/string.h:141:39: note: expected ‘char * restrict’ but argument is of type ‘char’
  141 | extern char *strcpy (char *__restrict __dest, const char *__restrict __src)
      |                      ~~~~~~~~~~~~~~~~~^~~~~~
main.c:41:23: warning: passing argument 1 of ‘strcpy’ makes pointer from integer without a cast [-Wint-conversion]
   41 |     strcpy(wtywtd.Face[100], "Prescription_Glasses");
      |            ~~~~~~~~~~~^~~~~
      |                       |
      |                       char
In file included from main.c:3:
/usr/include/string.h:141:39: note: expected ‘char * restrict’ but argument is of type ‘char’
  141 | extern char *strcpy (char *__restrict __dest, const char *__restrict __src)
      |                      ~~~~~~~~~~~~~~~~~^~~~~~

问题根源 #

1. 初始写法错误：&wtywtd.Footwear[100]是取数组第101个元素的地址（数组下标从0开始，Footwear[100]已经超出数组0-99的合法范围），直接越界写入到结构体的其他内存区域，触发栈溢出。
2. 移除&后的错误：wtywtd.Footwear[100]是取数组越界位置的单个char值，而strcpy要求第一个参数是char*类型的指针，因此出现类型不匹配警告。

修复方案 #

直接传递数组名作为strcpy的第一个参数——数组名本身就是指向数组首元素的指针，符合strcpy对char*类型参数的要求。

修正后的代码 #

//Reviewing structures
#include <stdio.h>
#include <string.h>

int main()
{
    struct date
    {
        int month;
        int day;
        int year;
    };
    
    struct date DateToday;
    DateToday.month = 5;
    DateToday.day = 7;
    DateToday.year = 2016;
    
    struct Outfit
    {
        char Footwear[100];
        char Bottoms[100];
        char Tops[100];
        char OverTop[100];
        char Face[100];
    };
    
    struct Outfit wtywtd;
    
    // 直接使用数组名作为strcpy的目标指针
    strcpy(wtywtd.Footwear, "Dark_Black_and_Gray_Nike_shoes");
    strcpy(wtywtd.Bottoms, "Dark_Beige_Cargo_Shorts");
    strcpy(wtywtd.Tops, "Dark_Red_And_Black_Striped_Tshirt");
    strcpy(wtywtd.OverTop, "Grey_Hooded_Fleece_Jacket");
    strcpy(wtywtd.Face, "Prescription_Glasses");
    
    printf("Todays date is %i/%i/%i", DateToday.month,DateToday.day,DateToday.year);
    printf("\nThe clothes I wore when going out were %s, %s, %s, %s, and %s", wtywtd.Footwear, wtywtd.Bottoms, wtywtd.Tops, wtywtd.OverTop, wtywtd.Face);
    
    return 0;
}

内容的提问来源于stack exchange，提问作者Jason Beswilan