c++ - 为什么要更改此字符串？

Question

我有以下代码，到目前为止，我想检查一个文件名是否已经在链表fileList(或flist)中。根据输出，保存在第一个节点中的字符串在 Node* getFileName(Node *&flist) 的某处发生了变化 这是怎么发生的？另外，关于 Node 和字符串的指针，我正在做的其他事情是否有错误或不安全？

输出:

in main: file4.txtstart of process: file4.txtfile4.txtmid of process: file4.txt"in contains, fileName in node: file4.txt"in contains, target file name: file4.txtend of process: file4.txt"0no recursive call

code:

struct Node {
    string fileName;
    Node *link;
};


/*
 *
 */
bool contains (Node *&flist, string &name) {
    Node *tempNode = *&flist;
    while (tempNode != 0) {
        cout << "in contains, fileName in node: " << flist->fileName << endl;
        cout << "in contains, target file name: " << name << endl;
        if ((tempNode->fileName) == name) {
            return true;
        }
        else {
            tempNode = tempNode->link;
        }
    }
    return false;
}


/*
 *
 */
Node* getLastNode (Node *&flist) {
    Node *tempNode = *&flist;
    while (tempNode != 0) {
        tempNode = tempNode->link;
    }
    return tempNode;
}


/*
 *
 */
string getFileName(string oneLine) {
    char doubleQuote;
    doubleQuote = oneLine[9];
    if (doubleQuote == '\"') {
        string sub = oneLine.substr(10);                    //getting the file name
        string::size_type n = sub.size();
        sub = sub.substr(0,n-1);
        cout <<  sub << endl;
        return sub;
    }
    return NULL;
}

/*
 *
 */
void process( istream &in, ostream &out, Node *&flist ) {
    cout << "start of process: " << flist->fileName << endl;
    string oneLine;         //temp line holder
    while (getline(in, oneLine)) {
        //      cout << oneLine << endl;
        string::size_type loc = oneLine.find("#include",0);
        if (loc != string::npos) {
            //found one line starting with "#include"
            string name;
            name = getFileName(oneLine);
            cout << "mid of process: " << flist->fileName << endl;
            bool recursive;
            recursive = contains(flist, name);
            cout << "end of process: " << flist->fileName << endl;
            cout << recursive << endl;
            if (recursive) {
                //contains recursive include
                cerr << "recursive include of file " << name << endl;
                exit(-1);
            }
            else {
                //valid include
                cout << "no recursive call" << endl;

            }//else
        }//if
    }//while

}//process
/*
 *
 */
int main( int argc, char *argv[] ) {
    istream *infile  = &cin;                            // default value
    ostream *outfile = &cout;                           // default value
    Node* fileList;

    switch ( argc ) {
    case 3:
        outfile = new ofstream( argv[2] );          // open the outfile file
        if ( outfile->fail() ) {
            cerr << "Can't open output file " << argv[2] << endl;
            exit( -1 );
        }
        // FALL THROUGH to handle input file
    case 2:
        infile = new ifstream( argv[1] );           // open the input file
        if ( infile->fail() ) {
            cerr << "Can't open input file " << argv[1] << endl;
            exit( -1 );
        }
        else {
            Node aFile = {argv[1], 0};
            fileList = &aFile;
            cout << "in main: " << fileList->fileName << endl;
        }
        // FALL THROUGH
    case 1:                                       // use cin and cout
        break;
    default:                                      // too many arguments
        cerr << "Usage: " << argv[0] << " [ input-file [ output-file ] ]" << endl;
        exit( -1 );                                 // TERMINATE!
    }

    processOneFile (*infile, *outfile, fileList);

    // do something
    if ( infile != &cin ) delete infile;              // close file, do not delete cin!
    if ( outfile != &cout ) delete outfile;           // close file, do not delete cout!
}

Answer 1

可以贴出原代码吗？您发布的代码甚至无法编译。

我注意到的错误，按顺序排列:

processOneFile (*infile, *outfile, fileList);

没有processOneFile()过程。

istream *infile  = &cin;                            // default value
ostream *outfile = &cout;                           // default value
Node* fileList;
case 1:                                       // use cin and cout
    break;
processOneFile (*infile, *outfile, fileList);

这将使用未初始化的文件列表调用 processOneFile()，当您尝试打印文件名时它会崩溃。

    else {
            Node aFile = {argv[1], 0};
            fileList = &aFile;
            cout << "in main: " << fileList->fileName << endl;
    }

aFile 仅在 else 范围内，因此稍后尝试使用指向它的指针将失败。

string getFileName(string oneLine) {
    ///
    return NULL;
}

你不能从 NULL 构造一个 std::string——这会导致程序崩溃。

在修复这些错误以使您的代码不会崩溃后，我无法重现错误。

如果您在 Linux 中构建，请尝试提高警告级别(使用 g++ -Wall -Wextra -ansi -pedantic)并通过 valgrind 运行您的代码，以检查内存错误。