为什么我会收到不匹配的错误？ （C ）

Question

我有这段代码，但找不到错误的来源。我想在 char 数组中存储多个名称，我必须使用 char 类型。我做了这个，但这有问题。

#include <iostream>
#define MAX 2
using namespace std;

int main()
{

    char **names;
    names=new char* [MAX];
    names[0]=new char[3];

    for(int i=0;i<3;i++)
       names[0][i]='a';

    names[1]=new char[4];
    cout<<names[0]<<endl;
    for(int i=0;i<4;i++)
        names[1][i]='b';

    cout<<names[1]<<endl;
    ////////////////
    for(int i=0;i<MAX;i++)
        delete names[i];
    delete [] names;
    return 0;
}

有人能解释一下为什么，我在 valgrind 中会出错吗？ 没有泄漏，但有错误。

Invalid read of size 1
==4063==    at 0x4C2BFB4: strlen (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==4063==    by 0x4EC62E0: std::basic_ostream<char, std::char_traits<char> >& std::operator<< <std::char_traits<char> >(std::basic_ostream<char, std::char_traits<char> >&, char const*) (in /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.16)
==4063==    by 0x400911: main (main.cpp:16)
==4063==  Address 0x5a03093 is 0 bytes after a block of size 3 alloc'd
==4063==    at 0x4C2AC27: operator new[](unsigned long) (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==4063==    by 0x4008B4: main (main.cpp:10)
==4063== 
aaa
==4063== Invalid read of size 1
==4063==    at 0x4C2BFB4: strlen (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==4063==    by 0x4EC62E0: std::basic_ostream<char, std::char_traits<char> >& std::operator<< <std::char_traits<char> >(std::basic_ostream<char, std::char_traits<char> >&, char const*) (in /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.16)
==4063==    by 0x400964: main (main.cpp:20)
==4063==  Address 0x5a030e4 is 0 bytes after a block of size 4 alloc'd
==4063==    at 0x4C2AC27: operator new[](unsigned long) (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==4063==    by 0x4008FA: main (main.cpp:15)
==4063== 
bbbb
==4063== Mismatched free() / delete / delete []
==4063==    at 0x4C2A4BC: operator delete(void*) (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==4063==    by 0x400992: main (main.cpp:23)
==4063==  Address 0x5a03090 is 0 bytes inside a block of size 3 alloc'd
==4063==    at 0x4C2AC27: operator new[](unsigned long) (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==4063==    by 0x4008B4: main (main.cpp:10)

Answer 1

您忘记了C-string 中的null terminator

names[0] = new char[4]; // 3 + 1 because of the null terminator

for(int i = 0; i < 3; i++)
   names[0][i] = 'a';

names[0][3] = '\0';

所以本质上，当您使用std::cout << 输出字符串时，valgrind 会报告无效的内存访问，因为输出例程不了解 C 字符串的结束位置，并且只是继续输出超出为细绳。

另外，我假设这是家庭作业或其他东西，否则你不使用 std::string 会发疯的。