c++ - 字符串流产生内存映射

Question

我在处理字符串流时遇到了一些问题；每当我尝试在非空字符串上使用操作符 (<<) 时，我都会在运行程序时打印内存映射。这是代码:

for(int i=1 ; i<djikstra_result[0] ; i++)
{
    cout << "DEBUG 5:10 - Round " << i << endl;
    if(i==djikstra_result[0]-1)
    {
        ss << djikstra_result[i] << "km.";
        cout << "DEBUG 5:11" << endl;
    }
    else
    {
        int j = djikstra_result[i];
        cout << "DEBUG 5:13 - j=" << j << endl;
        ss << this->airport[j] << " - ";
        cout << "DEBUG 5:14" << endl;
    }
}

ss是我的stringstream，djikstra_result[]是一个动态int数组，this-airport[]是一个动态字符串数组。

代码编译得很好，但它只运行到 "cout << "DEBUG 5:13 - j="<< j << endl;"。从那一点开始的结果是:

DEBUG 5:13 - j=0*** glibc detected *** ./graph: malloc(): memory corruption: 0x0000000000ec10f0 ***======= Backtrace: =========/lib/libc.so.6(+0x77806)[0x7f9f8403a806]/lib/libc.so.6(+0x7b928)[0x7f9f8403e928]/lib/libc.so.6(__libc_malloc+0x6e)[0x7f9f8403f7de]/usr/lib/libstdc++.so.6(_Znwm+0x1d)[0x7f9f848ab24d]/usr/lib/libstdc++.so.6(_ZNSs4_Rep9_S_createEmmRKSaIcE+0x59)[0x7f9f84887d79]/usr/lib/libstdc++.so.6(_ZNSs4_Rep8_M_cloneERKSaIcEm+0x2b)[0x7f9f8488874b]/usr/lib/libstdc++.so.6(_ZNSs7reserveEm+0x3c)[0x7f9f8488927c]/usr/lib/libstdc++.so.6(_ZNSs6appendERKSs+0x4f)[0x7f9f848896ff]./graph[0x402138]./graph[0x4032ce]/lib/libc.so.6(__libc_start_main+0xfd)[0x7f9f83fe1c4d]./graph[0x401439]======= Memory map: ========00400000-00404000 r-xp 00000000 00:15 15341576                           /home/psyberion/Dropbox/algorithms/assign-3b/graph00604000-00605000 r--p 00004000 00:15 15341576                           /home/psyberion/Dropbox/algorithms/assign-3b/graph00605000-00606000 rw-p 00005000 00:15 15341576                           /home/psyberion/Dropbox/algorithms/assign-3b/graph00ec1000-00ee2000 rw-p 00000000 00:00 0                                  [heap]7f9f7c000000-7f9f7c021000 rw-p 00000000 00:00 0 7f9f7c021000-7f9f80000000 ---p 00000000 00:00 0 7f9f83fc3000-7f9f8413d000 r-xp 00000000 08:05 2887651                    /lib/libc-2.11.1.so7f9f8413d000-7f9f8433c000 ---p 0017a000 08:05 2887651                    /lib/libc-2.11.1.so7f9f8433c000-7f9f84340000 r--p 00179000 08:05 2887651                    /lib/libc-2.11.1.so7f9f84340000-7f9f84341000 rw-p 0017d000 08:05 2887651                    /lib/libc-2.11.1.so7f9f84341000-7f9f84346000 rw-p 00000000 00:00 0 7f9f84346000-7f9f8435c000 r-xp 00000000 08:05 2884391                    /lib/libgcc_s.so.17f9f8435c000-7f9f8455b000 ---p 00016000 08:05 2884391                    /lib/libgcc_s.so.17f9f8455b000-7f9f8455c000 r--p 00015000 08:05 2884391                    /lib/libgcc_s.so.17f9f8455c000-7f9f8455d000 rw-p 00016000 08:05 2884391                    /lib/libgcc_s.so.17f9f8455d000-7f9f845df000 r-xp 00000000 08:05 2887634                    /lib/libm-2.11.1.so7f9f845df000-7f9f847de000 ---p 00082000 08:05 2887634                    /lib/libm-2.11.1.so7f9f847de000-7f9f847df000 r--p 00081000 08:05 2887634                    /lib/libm-2.11.1.so7f9f847df000-7f9f847e0000 rw-p 00082000 08:05 2887634                    /lib/libm-2.11.1.so7f9f847e0000-7f9f848d6000 r-xp 00000000 08:05 25175504                   /usr/lib/libstdc++.so.6.0.137f9f848d6000-7f9f84ad6000 ---p 000f6000 08:05 25175504                   /usr/lib/libstdc++.so.6.0.137f9f84ad6000-7f9f84add000 r--p 000f6000 08:05 25175504                   /usr/lib/libstdc++.so.6.0.137f9f84add000-7f9f84adf000 rw-p 000fd000 08:05 25175504                   /usr/lib/libstdc++.so.6.0.137f9f84adf000-7f9f84af4000 rw-p 00000000 00:00 0 7f9f84af4000-7f9f84b14000 r-xp 00000000 08:05 2887636                    /lib/ld-2.11.1.so7f9f84ceb000-7f9f84cef000 rw-p 00000000 00:00 0 7f9f84d10000-7f9f84d13000 rw-p 00000000 00:00 0 7f9f84d13000-7f9f84d14000 r--p 0001f000 08:05 2887636                    /lib/ld-2.11.1.so7f9f84d14000-7f9f84d15000 rw-p 00020000 08:05 2887636                    /lib/ld-2.11.1.so7f9f84d15000-7f9f84d16000 rw-p 00000000 00:00 0 7fff9500a000-7fff9501f000 rw-p 00000000 00:00 0                          [stack]7fff951ff000-7fff95200000 r-xp 00000000 00:00 0                          [vdso]ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0                  [vsyscall]Aborted

I have encountered this problem before, but I haven't been able to work out what's causing it, other than some kind of memory problem. Could someone please help?Here's the code for the whole function:

string graph::get_shortest(string name1, string name2)
{
int* djikstra_result;
int result[this->nr_airport];
int source=-1;
int goal=-1;
bool source_found = false;
bool goal_found = false;
string final="";
string space=" - ";
stringstream ss;
cout << "DEBUG 5:1" << endl;
for(int i=0 ; i<this->nr_airport ; i++)
{
    cout << "DEBUG 5:2 - Round " << i << endl;
    if(name1==this->airport[i])
    {
        cout << "DEBUG 5:3" << endl;
        source = i;
        source_found = true;
    }
    else if(name2==this->airport[i])
    {
        cout << "DEBUG 5:4" << endl;
        goal = i;
        goal_found = true;
    }
}
cout << "DEBUG 5:5" << endl;
if(!source_found || !goal_found)
{
    throw "Starting point or destination not found";
}
cout << "DEBUG 5:6" << endl;
for(int i=0 ; i<this->nr_airport ; i++)
{
    result[i] = -1;
    cout << "DEBUG 5:7 - Round " << i << endl;
}
cout << "DEBUG 5:8" << endl;
djikstra_result = djikstra(source, goal);
cout << "DEBUG 5:9" << endl;
for(int i=1 ; i<djikstra_result[0] ; i++)
{
    cout << "DEBUG 5:10 - Round " << i << endl;
    if(i==djikstra_result[0]-1)
    {
        ss << djikstra_result[i] << "km";
        cout << "DEBUG 5:11" << endl;
    }
    else
    {
        int j = djikstra_result[i];
        cout << "DEBUG 5:13 - j=" << j << endl;
        //string val = this->airport[j];
        cout << "DEBUG 5:14" << endl;
        ss << this->airport[j];
        cout << "DEBUG 5:15" << endl;
    }
}
ss >> final;
return final;   
}

编辑:

数组 this->airport[] 声明如下:

this->cap_airport = 1;
this->airport = new string[this->cap_airport];

当我向数组添加内容时，我使用以下函数扩展它:

void graph::expand_list()
{
if(this->nr_airport==this->cap_airport)
{
    this->cap_airport++;
    string* temp = new string[this->cap_airport];
    for(int i=0 ; i<this->nr_airport ; i++)
    {
        temp[i] = "";
        if(this->airport[i]!="")
        {
            temp[i] = this->airport[i];
        }
    }
    delete [] this->airport;
    this->airport = temp;
}
}

我这样做是为了避免分配比需要更多的空间，并且我只在从文件读取时向数组添加信息。

编辑:

从字符串中删除 << "- "; 后，似乎取得了一些进展。我在主函数中调用函数 get_shortest(string name1, string name2)，如下所示:

graph g1;
cout << g1.get_shortest("A","E") << endl;

我现在可以在运行程序时看到更多输出:

DEBUG 5:15DEBUG 5:10 - Round 5DEBUG 5:11AAAA0km*** glibc detected *** ./graph: free(): invalid pointer: 0x0000000001ba7070 ***======= Backtrace: =========/lib/libc.so.6(+0x77806)[0x7f400d9cf806]/lib/libc.so.6(cfree+0x73)[0x7f400d9d60d3]//And so on as before

所以问题似乎与字符串流本身无关。有什么想法吗？

Answer 1

我在程序的其他部分发现了问题；内存映射是无效内存操作的结果，但它并没有像建议的那样从 djikstra_result[] 或 this->airport[] 中读取。试图从数组中的无效位置读取会导致段错误。问题是我在函数 djikstra(int source, goal) 中试图将数据添加 到数组中的无效位置。这是代码:

result = new int[nr_visited];
for(int i=0 ; i<nr_visited+2 ; i++)
{
    if(i==0)
    {
        result[i] = nr_visited;
    }
    else if(i==nr_visited+1)
    {
        result[i] = distance;
    }
    else
    {
        result[i] = route[i-1];
    }
}
return result;

我创建了一个长度为nr_visited的动态int数组，但是我尝试将数据放在nr_visited+1的位置，这是无效的。这会导致内存映射。因此，修复方法是声明长度为 nr_visited+2 的 int 数组:

result = new int[nr_visited+2];

现在，一切正常。