Question

我将一个字符串或一个char数组传递给一个函数并交换它们但由于某种原因丢失了第一个char数组的值。这是我的代码：

void foo(char* a, char* b){

         char* temp;

         temp = new char[strlen(a)+1];
         strcpy(temp, a);
         strcpy(a, b);
         strcpy(b, temp);

         delete[] temp;
}

所以在foo中，函数会传递两个指针并尝试交换。这是主要功能。传递变量可能存在问题，但编译器没有给我一个问题。

int main(){

         char a[] = "First";
         char b[] = "Last";

         std::cout << "A Before: "<< a << "\n";
         std::cout << "B Before: " << b << "\n\n";

         foo(a, b);

         std::cout << "A After: "<< a << "\n";
         std::cout << "B After: "<< b << "\n\n";

         return 0;
}

我得到的输出如下：

A Before: first
B Before: last

A After: 
B After: first

现在我已经在strcpy的函数中测试了字符串的值，并在最后的strcpy之后变为空，这意味着，或者至少我认为，问题在于指向原始变量的指针。它可能是一种连锁反应类型的东西，其中所有指针都指向“a”并且它使程序混乱。

任何帮助都会受到赞赏，为什么这种情况发生也会非常有用。

Answer 1

因为您的字符串a超过了b。所以strcpy无法按预期排列：

strcpy(b, temp);

提示：

使用strncpy代替strcpy
使用c ++ Strings代替c样式字符串。然后你可以交换他们使用a.swap(b);

Answer 2

问题是你的数组大小碰巧正在破坏你的堆栈;幸运的是，对你而言，效果只是在a的第一个字符中放置一个空字节，使其成为一个空字符串。

#include <iostream>
#include <string.h>

void foo(char* a, char* b){
         char* temp = new char[strlen(a)+1];

         strcpy(temp, a);
         std::cout << "temp = " << temp << " a = " << a << " b = " << b << std::endl;

         strcpy(a, b);
         std::cout << "temp = " << temp << " a = " << a << " b = " << b << std::endl;

         strcpy(b, temp); // this copies 6 bytes to b, which puts a 0 in the first byte of a.
         std::cout << "temp = " << temp << " a = " << a << " b = " << b << std::endl;

         delete[] temp;
}

int main() {
     char a[] = "First";
     char b[] = "Last";

     std::cout << "a size is " << sizeof(a) << std::endl;
     std::cout << "b size is " << sizeof(b) << std::endl;

     std::cout << "address of a[0] is " << (void*)&a[0] << std::endl;
     std::cout << "address of b[0] is " << (void*)&b[0] << std::endl;

     foo(a, b);

     std::cout << "A After: "<< a << "\n";
     std::cout << "B After: "<< b << "\n\n";
}

http://ideone.com/fDvnnH

a size is 6
b size is 5
address of a[0] is 0xbfec5caa
address of b[0] is 0xbfec5ca5
temp = First a = First b = Last
temp = First a = Last b = Last
temp = First a =  b = First
A After: 
B After: First

您可能需要调查std::string或查看使用std::strncpy

传递给函数的C ++ strcpy指针

2 个答案: