为啥要更改此字符串？
Posted
技术标签:
【中文标题】为啥要更改此字符串？【英文标题】：Why is this string changed?为什么要更改此字符串？ 【发布时间】：2009-10-11 18:14:07 【问题描述】：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) 某处发生了更改这是怎么发生的？另外，关于节点和字符串的指针，我做的还有什么是错误的或不安全的吗？
输出：
在主要：file4.txt 进程开始：file4.txt 文件4.txt 进程中间：file4.txt" 包含，节点中的文件名：file4.txt" 在包含，目标文件名：file4.txt 进程结束：file4.txt" 0 没有递归调用代码：
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!
【问题讨论】：
您是否尝试过使用调试器单步执行您的代码？它应该比使用print 语句来显示哪个语句更改了您的数据更成功。
能否请您提供编译此文件所需的文件？
我还建议使用 std::set 来维护文件名而不是自制列表。
【参考方案1】：
您可以发布原始代码吗？您发布的代码甚至无法编译。
我注意到的错误，按顺序：
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会崩溃。
else
Node aFile = argv[1], 0;
fileList = &aFile;
cout << "in main: " << fileList->fileName << endl;
aFile 仅在该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;
您不能从NULL 构造std::string——这会使程序崩溃。
修复这些错误以使您的代码不会崩溃后，我无法重现该错误。
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。
【讨论】：
另外，没有所谓的“getFileName(Node *&flist)”这样的函数可能会导致问题。只有一个“getFileName(string oneLine)”，但这不可能改变其中一个节点中的字符串。 你可以从NULL初始化一个字符串。该字符串将为空。 @GMan：不，从NULL 初始化 std::string 是未定义的。在我的系统（和键盘，codepad.org/ZldIZHwo）上，它引发了一个异常。【参考方案2】：
好的，现在代码看起来确实像预期的那样工作：
#include <iostream>
#include <fstream>
using namespace::std;
struct Node
string fileName;
Node *link;
;
bool contains (Node *&flist, string &name)
Node *tempNode = *&flist;
while (tempNode != 0)
cout << "Searching in \"" << flist->fileName;
cout << "\" for \"" << 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);
return sub;
return "";
void process( istream &in, ostream &out, Node *&flist )
cout << "Start of process: " << flist->fileName << endl << endl;
string oneLine;
while (1)
cout << "Input include statement: ";
getline(in, oneLine);
if (oneLine == "STOP")
return;
string::size_type loc = oneLine.find("#include",0);
if (loc != string::npos)
//found one line starting with "#include"
string name;
name = getFileName(oneLine);
if (name == "")
cout << "Couldn't find filename, skipping line..." << endl;
continue;
if (contains(flist, name))
//contains recursive include
cerr << "Uh, oh! Recursive include of file " << name << endl;
exit(-1);
else
cerr << "No recursive include" << endl;
//if
cout << endl;
//while
int main( int argc, char *argv[] )
Node* fileList = new Node;
istream *infile = &cin; // default value
ostream *outfile = &cout; // default value
fileList->fileName = "Input"; // default value
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
fileList->fileName = argv[1];
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!
process(*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!
【讨论】：
【参考方案3】：另外，既然标准库已经有一个完美的链表，为什么还要浪费时间编写自己的链表？
【讨论】：
以上是关于为啥要更改此字符串？的主要内容，如果未能解决你的问题，请参考以下文章