C++ 中附加的 char* 的奇怪输出

Question

我只是在写简单的代码，然后我看到了一些奇怪的东西。该代码应该将一个字符串附加到另一个字符串。新附加字符串的输出不仅输出正确的附加字符串，而且每次四次都加上数字 2，我不明白为什么。我以为是我忽略了一些内存泄漏或类似的东西，但它每次都输出相同的四个数字。

代码：

#include <iostream>

using namespace std;


unsigned int getStrSize(const char* string)
{
    unsigned int size = 0;
    while (string[size] != '[=10=]')
    {
        size++;
    }
    return size;
}

int main()
{
    const char* bla1 = "hello";
    const char* bla2 = " blaah";

    int size1 = getStrSize(bla1);
    int size2 = getStrSize(bla2);
    int size12 = size1 + size2;

    char* bla12 = new char[size12];

    for (int i = 0; i < size1; i++)
    {
        bla12[i] = bla1[i];
    }
    for (int i = 0; i < size2; i++)
    {
        bla12[i + size1] = bla2[i];
    }
    char* blaNew = bla12;

    cout << bla1 << "\n";
    cout << bla2 << "\n";
    cout << bla12 << "\n";
    cout << blaNew << "\n";
}

输出：

hello
 blaah
hello blaah²²²²
hello blaah²²²²

Answer 1

你错过了零：

#include <iostream>

using namespace std;
unsigned int getStrSize(const char* string)
{
    unsigned int size = 0;
    while (string[size] != '[=10=]')
    {
        size++;
    }
    return size;
}

int main()
{
    const char* bla1 = "hello";
    const char* bla2 = " blaah";

    int size1 = getStrSize(bla1);
    int size2 = getStrSize(bla2);
    int size12 = size1 + size2 + 1; // notice +1

    char* bla12 = new char[size12];

    for (int i = 0; i < size1; i++)
    {
        bla12[i] = bla1[i];
    }
    for (int i = 0; i < size2; i++)
    {
        bla12[i + size1] = bla2[i];
    }
    bla12[size12 - 1] = '[=10=]'; // terminate with nil
    char* blaNew = bla12;

    cout << bla1 << "\n";
    cout << bla2 << "\n";
    cout << bla12 << "\n";
    cout << blaNew << "\n";

    delete[] bla12;  // Don't leak memory
    delete[] blaNew; // 
}

最好考虑使用标准库函数：

#include <cstring>
#include <iostream>

int main() {
  const char* bla1 = "hello";
  const char* bla2 = " blaah";

  auto const size1 = std::strlen(bla1);
  auto const size2 = std::strlen(bla2);
  auto const size12 = size1 + size2 + 1;

  char* bla12 = new char[size12];

  std::strcpy(bla12, bla1);
  std::strcat(bla12, bla2);
  char* blaNew = bla12;

  std::cout << bla1 << "\n";
  std::cout << bla2 << "\n";
  std::cout << bla12 << "\n";
  std::cout << blaNew << "\n";

  delete[] bla12;
  delete[] blaNew;
}

Answer 2

问题是您没有以 null 终止您的 char* 缓冲区。 std::cout.operator<<(char*) 将尝试找到 [=11=] 作为其终止字符。所以你只需要在缓冲区的末尾附加 [=11=] 。

注意：注意增加buffer 1的大小，否则你会access/write一个未分配的内存。

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