EXC_BAD_ACCESS-C ++ substr函数

如何解决EXC_BAD_ACCESS-C ++ substr函数

我有一个使用c ++ substr的函数。在Linux和macOS上，此功能有时会在程序末尾（从单独的线程调用时）随机崩溃。

功能如下：

bool mkpath( string path )
{
bool bSuccess = false;
int nRC = ::mkdir( path.c_str(),0775 );
if( nRC == -1 )
{
    switch( errno )
    {
        case ENOENT:
            //parent didn't exist,try to create it
            if( mkpath( path.substr(0,path.find_last_of('/')) ) )
            {
                //Now,try to create again.
                int status = ::mkdir( path.c_str(),0775 );
                bSuccess = (0 == status || errno == EEXIST);
            }
            else
            {
                bSuccess = false;
            }
            break;
        case EEXIST:
            //Done!
            bSuccess = true;
            break;
        default:
            bSuccess = false;
            break;
    }
}
else
    bSuccess = true;
return bSuccess;
}

lldb回溯如下：

* thread #4,stop reason = EXC_BAD_ACCESS (code=2,address=0x70000097fff8)
* frame #0: 0x00007fff73d2a81a libsystem_malloc.dylib`tiny_malloc_from_free_list + 8
frame #1: 0x00007fff73d2a297 libsystem_malloc.dylib`tiny_malloc_should_clear + 288
frame #2: 0x00007fff73d290c6 libsystem_malloc.dylib`szone_malloc_should_clear + 66
frame #3: 0x00007fff73d27d7a libsystem_malloc.dylib`malloc_zone_malloc + 104
frame #4: 0x00007fff73d27cf5 libsystem_malloc.dylib`malloc + 21
frame #5: 0x00007fff70ea0dea libc++abi.dylib`operator new(unsigned long) + 26
frame #6: 0x00007fff70e73d70 libc++.1.dylib`std::__1::basic_string<char,std::__1::char_traits<char>,std::__1::allocator<char> 
>::basic_string(std::__1::basic_string<char,std::__1::allocator<char> > const&,unsigned long,std::__1::allocator<char> 
const&) + 132
frame #7: 0x0000000103821467 libSampleLibrary.dylib`std::__1::basic_string<char,std::__1::allocator<char> >::substr(unsigned long,unsigned 
long) const + 87
frame #8: 0x0000000103820c77 libSampleLibrary.dylib`mkpath(std::__1::basic_string<char,std::__1::allocator<char> >) + 135
frame #9: 0x0000000103820c80 libSampleLibrary.dylib`mkpath(std::__1::basic_string<char,std::__1::allocator<char> >) + 144
frame #10: 0x0000000103820c80 libSampleLibrary.dylib`mkpath(std::__1::basic_string<char,std::__1::allocator<char> >) + 144
frame #11: 0x0000000103820c80 libSampleLibrary.dylib`mkpath(std::__1::basic_string<char,std::__1::allocator<char> >) + 144
frame #12: 0x0000000103820c80 libSampleLibrary.dylib`mkpath(std::__1::basic_string<char,std::__1::allocator<char> >) + 144
frame #13: 0x0000000103820c80 libSampleLibrary.dylib`mkpath(std::__1::basic_string<char,std::__1::allocator<char> >) + 144
frame #14: 0x0000000103820c80 libSampleLibrary.dylib`mkpath(std::__1::basic_string<char,std::__1::allocator<char> >) + 144
frame #15: 0x0000000103820c80 libSampleLibrary.dylib`mkpath(std::__1::basic_string<char,std::__1::allocator<char> >) + 144
...

发生这种情况的任何可能原因？像我们添加的那样，可以从外部取消调用该线程的线程

pthread_setcanceltype（PTHREAD_CANCEL_ASYNCHRONOUS，NULL）;

在函数的第一行，从该函数被调用。

无论何时发生此崩溃，我都会在回溯中看到以下行超过5400次，这非常令人惊讶：

frame #15: 0x0000000103820c80 libSampleLibrary.dylib`mkpath(std::__1::basic_string<char,std::__1::allocator<char> >) + 144

我进一步调试，结果发现一个静态变量（homePath）被破坏（返回垃圾）。 mkpath（）函数从以下函数获取它的值：

string GetSettingFilePath()
{
    static string homePath = "";
    if(!homePath.empty()){
        
        // sometimes homePath variable returns junk at the program exit
        return homePath;
    }

    struct passwd* pwd = getpwuid(getuid());

    if (pwd)
    {
        homePath = pwd->pw_dir;
    }
    else
    {
        // try the $HOME environment variable
        homePath = getenv("HOME");
    }
    if (homePath.empty())
    {
        homePath = "./";
    }
    return homePath
}

由于尽管正确设置了homePath变量，有时它会在程序退出时返回垃圾，所以会导致无限递归。但是，为什么在程序出口调用该函数时，该函数内部的静态变量会返回垃圾。

解决方法

如果您递归调用mkpath，而path中的字符串 中没有斜杠/。那么您将拥有无限递归。

递归将是无限的，因为您将使用与调用时完全相同的参数调用mkpath。

在进行递归调用之前，应检查path是否真的有斜杠/。