C++指针练习代码抛出std::bad_alloc异常问题求助及优化建议

问题背景 #

为练习C++指针编写字符串单词搜索代码，初始版本可正常运行。为实现解耦并练习指针传参，将功能拆分到全局函数后，控制台持续抛出异常：

(C++) terminate called after throwing an instance of 'std::bad_alloc' what(): std::bad_alloc

无法运行的版本代码 #

#include <iostream>
#include <cstring>
using namespace std;

int serching(char*a , const char* b, const int n); // repeating serching desginated word in the ariticle.

int target(char*& a, int& b); // Let users enter a word.

int main()
{
    int timesA = 1; //recording the numbers of total words in article.
    int timesD = 0; //recording the numbers of designated words.
    const int maxlength = 10000;
    char a[maxlength];
    
    cout << "Please enter the paragraph less than " << maxlength <<  " characters. " << endl;
    
    cin.getline(a, maxlength);
    size_t l = strlen(a);
    
    cout << "Total numbers of characters: " << l << endl;
    
    char* aptr = new char [l]; 
    for(int i = 0; i < l; i++)
    {
        aptr[i] = a[i];
    }
    
    int n;
    char* desg;
    int num = target(desg, n);
    serching(aptr, desg, num);
        
    delete[] desg;
    desg = 0;
        
    cout << "There are " << timesD << " designated words found in this paeagraph. " << endl;
    
        
    delete[] aptr;
    aptr = 0;
    
    return 0;
} 

int serching(char*a , const char* b, const int n) 
{
    int num = 0;
    char* i  = strstr(a, b);
    while(i != 0)
    {
        num++;
        i = strstr((i + n), b);
    }
    delete[] i;
    i = 0;
    return num;
}

int target(char*& a, int& b)
{
    a = new char[b];
    cout << "Please enter a word: " << endl;
    cin.getline(a, 20);
    b = strlen(a);
    delete[] a;
    a = 0;
    return b;
}

可正常执行的原始版本代码 #

#include <iostream>
#include <cstring>
using namespace std;

int main()
{
    int timesA = 1; //recording the numbers of total words in article.
    int timesD = 0; //recording the numbers of designated words.

    const int maxlength = 10000;    
    char a[maxlength];
    
    cout << "Please enter the paragraph less than " << maxlength <<  " characters. " << endl;
    
    cin.getline(a, maxlength);
    size_t l = strlen(a);
    
    cout << "Total numbers of characters: " << l << endl;
    
    char* aptr = new char [l]; //pass into a dynamic array, for I'm practcing this.
    for(int i = 0; i < l; i++)
    {
        aptr[i] = a[i];
    }

    int n;
    char* desg = new char[n]; 
    cout << "Please enter a word: " << endl;
    cin.getline(desg, 20); 
    n = strlen(desg);
        
        
    char* i  = strstr(aptr, desg); // repeating serching the word in the string.
    while(i != 0)
    {
        timesD++;
        i = strstr((i + n), desg);
    }
    delete[] i;
    i = 0;
    delete[] desg;
    desg = 0;
        
    cout << "There are " << timesD << " designated words found in this paeagraph. " << endl;
    
    delete[] aptr;
    aptr = 0;

    return 0;
} 

问题排查 #

1. target函数的致命错误

   • 传入的int& b未初始化，a = new char[b];中b是随机垃圾值，可能是极大的数值，直接触发std::bad_alloc异常
   • 刚分配内存就执行delete[] a;并将a置空，导致main函数中desg变为空指针，后续serching函数调用strstr时传入空指针，引发未定义行为
   • cin.getline(a,20)中，a的大小是未初始化的b，若b小于20会导致缓冲区溢出

2. serching函数的错误

   • strstr返回的是指向原字符串内部的指针，并非通过new分配的内存，执行delete[] i;会触发未定义行为

3. main函数的问题

   • 未接收serching函数的返回值，timesD始终为0，输出结果错误
   • aptr = new char[l];只分配了l个字符空间，但原字符串a的长度是l，未预留结束符'\0'的位置，导致strlen和strstr读取越界

编程风格与代码优化建议 #

• 替换C风格字符串为std::string：完全避免手动内存管理，消除内存泄漏、越界、未初始化等问题，代码更简洁安全
• 规范函数设计：target函数应负责创建并返回目标字符串，而非通过混乱的指针传参传递结果；函数命名修正拼写错误，如serching改为search，desginated改为designated
• 初始化所有变量：避免未初始化变量导致的随机行为，比如原始版本中int n;未初始化就用于分配内存，属于侥幸运行
• 禁止释放非动态分配的指针：strstr返回的指针属于原字符串，无需手动释放
• 避免using namespace std;：防止全局命名空间污染，明确标注std库组件，如std::cout、std::string
• 添加输入校验：执行cin.getline后检查输入是否成功，避免异常输入导致的错误
• 简化逻辑：原始版本中timesA变量未被使用，可直接删除；动态复制字符串可使用strcpy（需预留结束符空间）或直接用std::string

内容的提问来源于stack exchange，提问作者Bevis000