将std::字符串数据的深层副本存储到std::vector中

Storing deep copies of std::string data into std::vector

本文关键字：std 存储 副本 vector 字符串 数据      更新时间：2023-10-16

我一定快疯了，但我正在遵循将std:：string转换为const char*或char*的示例，并且我在valgrind中得到了很多Invalid read of size 1。我基本上是在尝试拆分空白分隔的字符串，并将它们存储到std::vector<const char*>中。我知道，因为从c_str()返回的指针随时可能无效，所以您必须执行复制才能安全地使用数据。但看来我一定是错过了什么，因为valgrind在抱怨。至少，我复制了最重要的答案并这样做：

#include <iostream>
#include <sstream>
#include <vector>
using namespace std;
int main()
{
    std::vector<const char*> args;
    std::string str = "hey";
    char * writable = new char[str.size() + 1];
    std::copy(str.begin(), str.end(), writable);
    writable[str.size()] = ''; // don't forget the terminating 0
    args.push_back(writable);
    delete[] writable;
    for (size_t i = 0; i < args.size(); ++i)
        cout << args[i] << "n";
    return 0;
}

这导致valgrind的以下输出：

==5297== Invalid read of size 1
==5297==    at 0x4C2BFC2: __GI_strlen (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==5297==    by 0x400CFF: main (in /tmp/1411705143.17426/a.out)
==5297==  Address 0x5c2a0a0 is 0 bytes inside a block of size 4 free'd
==5297==    at 0x4C2A09C: operator delete[](void*) (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==5297==    by 0x400CD9: main (in /tmp/1411705143.17426/a.out)
==5297== 
==5297== Invalid read of size 1
==5297==    at 0x4C2BFD4: __GI_strlen (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==5297==    by 0x400CFF: main (in /tmp/1411705143.17426/a.out)
==5297==  Address 0x5c2a0a1 is 1 bytes inside a block of size 4 free'd
==5297==    at 0x4C2A09C: operator delete[](void*) (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==5297==    by 0x400CD9: main (in /tmp/1411705143.17426/a.out)
==5297== 
==5297== Invalid read of size 1
==5297==    at 0x58E6DB8: _IO_default_xsputn (genops.c:480)
==5297==    by 0x58E4D19: _IO_file_xsputn@@GLIBC_2.2.5 (fileops.c:1393)
==5297==    by 0x58DA98C: fwrite (iofwrite.c:45)
==5297==    by 0x4EC8A35: std::basic_ostream<char, std::char_traits<char> >& std::__ostream_insert<char, std::char_traits<char> >(std::basic_ostream<char, std::char_traits<char> >&, char const*, long) (streambuf:451)
==5297==    by 0x400D0F: main (in /tmp/1411705143.17426/a.out)
==5297==  Address 0x5c2a0a0 is 0 bytes inside a block of size 4 free'd
==5297==    at 0x4C2A09C: operator delete[](void*) (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==5297==    by 0x400CD9: main (in /tmp/1411705143.17426/a.out)
==5297== 
==5297== Invalid read of size 1
==5297==    at 0x58E6DC7: _IO_default_xsputn (genops.c:479)
==5297==    by 0x58E4D19: _IO_file_xsputn@@GLIBC_2.2.5 (fileops.c:1393)
==5297==    by 0x58DA98C: fwrite (iofwrite.c:45)
==5297==    by 0x4EC8A35: std::basic_ostream<char, std::char_traits<char> >& std::__ostream_insert<char, std::char_traits<char> >(std::basic_ostream<char, std::char_traits<char> >&, char const*, long) (streambuf:451)
==5297==    by 0x400D0F: main (in /tmp/1411705143.17426/a.out)
==5297==  Address 0x5c2a0a2 is 2 bytes inside a block of size 4 free'd
==5297==    at 0x4C2A09C: operator delete[](void*) (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==5297==    by 0x400CD9: main (in /tmp/1411705143.17426/a.out)
==5297==

我怀疑这个解决方案不起作用，因为向量中的数据在删除后指向垃圾。我也试过args.push_back(std::move(writable))。什么是变通方法？

这个例子说"不要忘记在使用字符串后释放它"。在将地址插入向量后，您立即对内存进行delete操作。当您稍后尝试访问相同的地址时，这会导致代码非常混乱。

在不讨论您的方法作为一个整体的优点（以及您为什么要做您正在做的事情）的情况下，问题的即时解决方案是只有在使用完向量中的地址后才调用delete。

请注意，您需要在向量上循环，并在向量中的每个地址上调用delete。

我决定让一个智能指针来处理我的内存。

std::vector<std::unique_ptr<char[]>> args;
std::string str = "hey";
char * writable = new char[str.size() + 1];
std::copy(str.begin(), str.end(), writable);
writable[str.size()] = ''; // don't forget the terminating 0
args.push_back(std::unique_ptr<char[]>(writable));

您遇到valgrind读取问题，因为在"cout<<args[i]<"\n"；"行读取"writible"之前已删除。

您应该在引用后将其删除。

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