C++ malloc代碼中的VC++ 2010錯誤

Question

請考慮VC++ 2010中的以下C代碼，用於在C語言中創建BST。通過在VC++項目中創建win32控制檯應用程序。

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

typedef struct BSTNode 
{ 
    char *data; 
    struct BSTNode *left,*right; 

}Node; 

Node *createNode(char *str) 
{ 
    int strLength=strlen(str); 
    char *data=(char *)malloc(strLength+1); 
    strcpy(data,str); 
    data[strLength+1]='\0'; 

    Node *temp=(Node *)malloc(sizeof(Node)); 
    temp->left=0; 
    temp->right=0; 
    temp->data=data; 

    return temp; 
} 

int main() 
{ 
    Node *root=createNode("Ravinder"); 

    printf("%s\n",root->data); 
    return 0; 
} 

它給出錯誤的VC++ 2010：

warning C4996: 'strcpy': This function or variable may be unsafe. Consider using strcpy_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS. See online help for details. c:\users\radha krishna\documents\visual studio 2010\projects\binarysearchtree\binarysearchtree\main.c 17 
warning C4047: 'return' : 'Node *' differs in levels of indirection from 'int' c:\users\radha krishna\documents\visual studio 2010\projects\binarysearchtree\binarysearchtree\main.c 25 
error C2275: 'Node' : illegal use of this type as an expression c:\users\radha krishna\documents\visual studio 2010\projects\binarysearchtree\binarysearchtree\main.c 20 
error C2223: left of '->right' must point to struct/union c:\users\radha krishna\documents\visual studio 2010\projects\binarysearchtree\binarysearchtree\main.c 22 
error C2223: left of '->left' must point to struct/union c:\users\radha krishna\documents\visual studio 2010\projects\binarysearchtree\binarysearchtree\main.c 21 
error C2223: left of '->data' must point to struct/union c:\users\radha krishna\documents\visual studio 2010\projects\binarysearchtree\binarysearchtree\main.c 23 
error C2065: 'temp' : undeclared identifier c:\users\radha krishna\documents\visual studio 2010\projects\binarysearchtree\binarysearchtree\main.c 20 
error C2065: 'temp' : undeclared identifier c:\users\radha krishna\documents\visual studio 2010\projects\binarysearchtree\binarysearchtree\main.c 21 
error C2065: 'temp' : undeclared identifier c:\users\radha krishna\documents\visual studio 2010\projects\binarysearchtree\binarysearchtree\main.c 22 

但是，如果我取代上述功能createnode通過這一點，做工精細：

Node *createNode(char *str) 
{ 
    Node *temp=(Node *)malloc(sizeof(Node)); 
    temp->left=0; 
    temp->right=0; 
    temp->data=str; 

    return temp; 
} 

Answer 1

MSVC 2010不支持現代C的方言，例如C99 - 它仍然只有C89，所以你需要把所有的變量聲明移到你函數的開頭，例如你的函數的清理版本可能是這樣的：

Node *createNode(const char *str) 
{ 
    int strLength = strlen(str); 
    char *data = malloc(strLength + 1); 
    Node *temp = malloc(sizeof(*temp)); 

    strcpy(data, str); 

    temp->left = NULL; 
    temp->right = NULL; 
    temp->data = data; 

    return temp; 
} 

注意有一個嚴重的錯誤在這裏：

data[strLength+1]='\0'; 

這將導致未分配的內存無效寫。

這應該是：

data[strLength]='\0'; 

但是這種操作是多餘的，無論如何，作爲strcpy將已經在字符串的結尾寫'\0'，所以你還不如干脆刪除這條線。

還請注意，您在許多地方投射了malloc的結果 - 這是redundant and potentially dangerous - 您應該移除這些投射。