跟踪在c ++代码gdb中的指针 [英] traceback a pointer in c++ code gdb
问题描述
我在运行c ++应用程序时遇到段错误。在gdb它显示我的一个指针位置被损坏的某种方式。但我有100万这样的对象指针在我的应用程序创建。我如何看一个导致崩溃
我可以在bt命令中查看指针的生命周期吗？
I am getting seg fault while running a c++ application. In gdb it shows somehow my one pointer location getting corrupted. But I have 100 thousands of such object pointers created during my application. How can I watch one which is causing the crash Can I do any operation in bt command to see the lifetime of that pointer?
感谢
Ruchi
Thanks Ruchi
推荐答案
我在过去有一些mem泄漏问题（由编译器错误）在应用程序中有大约256K指针，所以我不得不检查它不知何故。经过一番斗争，我创建了一个表的所有分配的指针及其大小和一些功能，以保持更新。结果是：
I had some mem-leaks problems in the past (caused by compiler bug) in apps with about 256K pointers so i had to check it somehow. After some struggle I created a table of all allocated pointers and their sizes and some functions to keep it updated. the result is this:
文件： mmap.h
//---------------------------------------------------------------------------
//--- Memory map system ver: 2.03 -------------------------------------------
//---------------------------------------------------------------------------
#ifndef _mmap_h
#define _mmap_h
//---------------------------------------------------------------------------
#define _mmap_aprox
//---------------------------------------------------------------------------
/*
new
#ifdef _mmap_h
if () mmap_new('Main',,sizeof());
#endif
#ifdef _mmap_h
if () mmap_del('Main',);
#endif
delete
*/
//---------------------------------------------------------------------------
struct _mmap_entry
{
char ids[4]; // id string
DWORD beg,end; // mem adr <beg,end)
_mmap_entry(){ beg=0; end=0; ((DWORD*)(ids))[0]='LLUN'; };
_mmap_entry(_mmap_entry& a) { *this=a; }
~_mmap_entry() {}
_mmap_entry* operator = (const _mmap_entry *a) { *this=*a; return this; }
//_mmap_entry* operator = (const _mmap_entry &a) { ...copy... return this; }
};
//---------------------------------------------------------------------------
const int _mmap_entries=4*1024; // max num of allocated memory chunks (pointers)
const int _mmapn_entries=32; // num of last news to remember
const int _mmapd_entries=32; // num of last dels to remember
static _mmap_entry mmap [_mmap_entries]; // memory map table active ptrs
static _mmap_entry mmapn[_mmapn_entries]; // memory map table last news
static _mmap_entry mmapd[_mmapd_entries]; // memory map table last dels
static int mmaps=0; // num of used entries in memory map table
static int mmapn_ix=0; // num of last deletes to remember
static int mmapd_ix=0; // num of last deletes to remember
static int mmap_errs=0; // error count
static int mmap_news=0; // allocations count
static int mmap_dels=0; // deallocations count
//---------------------------------------------------------------------------
void mmap_err(const char* msg,DWORD ptr) // breakpointeable error
{
mmap_errs++;
}
//---------------------------------------------------------------------------
int mmap_new(DWORD ids,void* ptr,DWORD siz) // tracks all allocations return false if error
{
mmap_news++;
int i,j; _mmap_entry e,*p;
e.beg=DWORD(ptr);
e.end=e.beg+siz;
e.ids[0]=((char*)&ids)[3];
e.ids[1]=((char*)&ids)[2];
e.ids[2]=((char*)&ids)[1];
e.ids[3]=((char*)&ids)[0];
if (e.beg==0)
{
mmap_err("Not enough memory.",e.beg);
return 0;
}
// find first i where mmap[i].end >= e.beg
#ifdef _mmap_aprox
if (!mmaps) i=0;
else{
for (j=1;j<mmaps;j<<=1); j>>=1; if (!j) j=1;
for (i=0;j;j>>=1)
{
i|=j;
p=mmap+i;
if ((i>=mmaps)||(e.beg<p->end)) i^=j;
if ((e.beg<p->end)&&(e.end>p->beg))
{
mmap_err("Bad allocation.",e.beg); // memory already allocated
return 0;
}
}
if (e.beg>=mmap[i].end) i++;
}
#endif
#ifndef _mmap_aprox
for (i=mmaps-1,p=mmap+i;i>=0;i--,p--)
if (e.beg<p->end)
{
if (e.end>p->beg)
{
mmap_err("Bad allocation.",e.beg); // memory already allocated
return 0;
}
} else break; i++;
#endif
// insert new pointer at i
if (mmaps>=_mmap_entries)
{
mmap_err("Too many pointers.",e.beg); // _mmap_entries is too low
return 0;
}
for (j=mmaps;j>i;j--) mmap[j]=mmap[j-1];
mmap[i]=e; mmaps++;
// remember last new in mmapn table
mmapn[mmapn_ix]=e; mmapn_ix++;
if (mmapn_ix>=_mmapn_entries) mmapn_ix=0;
return 1;
};
//---------------------------------------------------------------------------
int mmap_del(DWORD ids,void* ptr) // tracks all deallocations return false if error
{
mmap_dels++;
int i,j; _mmap_entry *p;
DWORD adr=DWORD(ptr);
if (adr==0)
{
mmap_err("Can not delete NULL.",adr);
return 0;
}
if (mmap<=0)
{
mmap_err("Nothing to delete.",adr);
return 0;
}
// find mmap[i] where beg==ptr and delete it if found
#ifdef _mmap_aprox
if (!mmaps) i=0;
else{
for (j=1;j<mmaps;j<<=1); j>>=1; if (!j) j=1;
for (i=0;j;j>>=1)
{
i|=j;
p=mmap+i;
if ((i>=mmaps)||(adr<p->beg)) i^=j;
}
if (adr==mmap[i].beg)
{
if (mmaps>1) for (j=i;j<mmaps-1;j++) mmap[j]=mmap[j+1];
mmaps--;
// remember last delete in mmapd table
mmapd[mmapd_ix]=mmap[mmaps]; mmapd_ix++;
if (mmapd_ix>=_mmapd_entries) mmapd_ix=0;
// delete ptr from mmap table
mmap[mmaps].beg=0;
mmap[mmaps].end=0;
return 1;
}
for (p=mmap,j=0;j<=i;j++,p++) // test all mmap[j].beg < adr
if (adr<p->end) // if overlap then ...
{
mmap_err("Wrong delete pointer.",adr); // pointer inside already allocated space
return 0;
}
}
#endif
#ifndef _mmap_aprox
for (p=mmap,i=0;i<mmaps;i++,p++)
if (p->beg==adr)
{
if (mmaps>1) for (j=i;j<mmaps-1;j++) mmap[j]=mmap[j+1];
mmaps--;
mmap[mmaps].beg=0;
mmap[mmaps].end=0;
return 1;
} else if (p->beg>adr) break;
for (p=mmap,i=0;i<mmaps;i++,p++)
if ((adr>p->beg)&&(adr<p->end))
{
mmap_err("Wrong delete pointer.",adr); // pointer inside already allocated space
return 0;
}
#endif
mmap_err("Delete pointer not found.",adr);
return 0;
};
//---------------------------------------------------------------------------
#endif
//---------------------------------------------------------------------------
//---------------------------------------------------------------------------
现在在您的代码中只需执行以下操作：
Now in your code just do this:
// edit the safe big enough number of pointers to use for your application in begin of the mmap.h
_mmap_entries=512*1024;
// before any delete/delete[] of pointer ptr add this:
#ifdef _mmap_h
if (ptr!=NULL) mmap_del('info',ptr);
#endif
if (ptr!=NULL) delete[] ptr;
// after any new of pointer ptr of size siz [byte] add this:
ptr=new BYTE[siz];
#ifdef _mmap_h
if (ptr!=NULL) mmap_new('info',ptr,siz);
#endif
所以如果你包括mmap.h !!
So if you include mmap.h as a first include !!!
- 在函数中放置断点void mmap_err（const char * msg，DWORD ptr）
- 运行应用程序
- 如果发生任何分配错误，它将在异常之前中断，因此您可以实际看到信息和种类关闭错误， li>
- place breakpoint inside function void mmap_err(const char* msg,DWORD ptr)
- run application
- if any allocation error occurs then it will break before exception so you can actually see the info and kind off error and also can step to code where error occurs
我是BDS2006 Turbo C ++用户，所以如果我忘了一些VCL东西只是转换为MSVC ++或评论我和我会做到，没有看到任何可能导致麻烦的事情。
I am BDS2006 Turbo C++ user so if I forgot some VCL stuff just convert it to MSVC++ or comment me and i will do it, but I don't see anything what could cause troubles.
PS。我发现我的编译器是一个致命错误：
PS. I found out that for my compiler is a fatal error to:
- 多次删除指针
- 没有正确的构造函数/析构函数的结构
在这两种情况下，没有异常被抛出，但是内存管理器后来被破坏，
in both cases no exception is thrown but memory manager is corrupted afterwards so it allocates wrongly hence exceptions
我的编译器的正确构造函数/析构函数
适用于所有将被动态分配的结构和类或其任何组件
是这样的：
Proper constructors/destructors for my compiler
for all structs and classes which will be dynamically allocated or any of their component
is like this:
class/struct T
{
public:
T() {}
T(T& a) { *this=a; }
~T() {}
T* operator = (const T *a) { *this=*a; return this; }
// if any dynamic allocation occur then this must be done also else not
//T* operator = (const T &a) { ... copy a to this ... return this; }
};
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