几个星期前，我第一次使用（我不习惯使用它们）浮动，双打，我在比较中遇到一些问题操作数。在尝试为这些类型赋值时我也遇到了问题，但我也解决了这个问题......
今天，我正在用C ++创建一个库，我发现了一个错误......好吧......很奇怪？或者只是我的愚蠢思考？
这是代码：
ini::ini(const char * path, bool _autoflush_ /*= false*/) {
/* Storing file name ... */
f_name = new char[strlen(path)+1];
strcpy(f_name, path);
/* Storing autoflush ... */
autoflush = _autoflush_;
/* First step: getting file size */
/* Open the file in read/append mode */
FILE * fd = fopen(path, "r");
/* On non-valid descriptor, goto next step directly */
if(fd == NULL) f_size = 1; goto allocbuffer;
/* Seek to the end */
fseek(fd, 0, SEEK_END);
/* Get file size */
f_size = (unsigned long int)ftell(fd) + 1;
/* Second step: allocating memory for the buffer */ allocbuffer:
cout << endl << endl << endl << endl << "Wanting " << sizeof(char)*f_size << " bytes of memory!" << endl << endl << endl << endl;
/* Allocate buffer-space */
buffer = (char*)malloc(sizeof(char)*f_size);
if(buffer == NULL) {
errord = (char*)malloc(strlen(INI_ERROR_NOT_ENOUGH_MEMORY) + 1);
strcpy(errord, INI_ERROR_NOT_ENOUGH_MEMORY);
cout << endl << endl << endl << endl << "Last error: \"" << errord << "\"." << endl << endl << endl << endl;
return;
}
/* Initialize and fill it with null bytes */
memset(buffer, 0, f_size);
/* Goto next step */
if(fd == NULL) goto endconstruct;
/* Third step: storing in the buffer */ loadbuffer:
/* Rewind file descriptor */
rewind(fd);
/* Read from file */
if(fread(buffer, 1, f_size, fd) != f_size) {
errord = (char*)malloc(strlen(INI_ERROR_NOT_READED) + 1);
strcpy(errord, INI_ERROR_NOT_READED);
cout << endl << endl << endl << endl << "Last error: \"" << errord << "\"." << endl << endl << endl << endl;
cout << endl << endl << endl << endl << "BYTES OF FILE: \"" << f_size << "\"." << endl << endl << endl << endl;
}
/* Close file descriptor */
fclose(fd);
/* Get number of lines */
f_line = strnum(buffer, "\n") + 1;
/* End building of object */
endconstruct:
/* Print out what is stored in the buffer NOW */
cout << endl << endl << endl << endl << "Buffer is:" << endl << buffer << endl << endl << endl << endl;
return;
}
可能已经创建了 ini 库，并且比我的好得多。但是我开始从C学习C ++，我想练习一些有趣且有用的东西。我错过了课堂宣言，我不知道是否有必要将其粘贴在这里，但这里是：
/** @def INI_ERROR_NOT_READED
@brief <em>Not readed as many bytes as required</em>
*/
#define INI_ERROR_NOT_READED "Not readed as many bytes as required"
/** @def INI_ERROR_NOT_ENOUGH_MEMORY
@brief <em>There is not enough memory</em>
*/
#define INI_ERROR_NOT_ENOUGH_MEMORY "There is not enough memory"
/** @class ini
@brief Class to describe <em>ini</em> files.
It describes an ini file. All the file is readed and loaded
in memory, for faster access. This class is the
improved & C++ version of the old, monstruous
functions defined in the old, monstruous IO Utilities
Library. Writting functions use dynamic memory reallocation
and file flush to the filesystem.
*/
class ini {
public:
/** @brief Constructor. Gives initial memory for the buffer and loads all the file in that buffer.
*
* @param path - Path of the <em>ini</em> file to open.
* @param _autoflush_ - Whether to auto-flush changes to hard disk or not.
* If you don't set it to any value, <em>false</em> is taked as default
* value and you have to flush changes manually using member function flush().
* Setting it to <em>true</em> may make it less efficient, so be careful
* if you're going to make a lot of changes in the <em>ini</em> file.
*/
ini (const char * path, bool _autoflush_ = false);
/** @brief Destructor. Frees the memory pointed by <em>buffer</em> and destroys the #ini object.
*
* It's very important to free the memory buffer, to avoid memory corruptions.
*/
~ini (void);
/** @brief Gets last error stored in private member <em>errord</em>.
*
* @return Last error-descriptor as string.
*/
char * geterror (void);
/** @brief Flush changes made in the buffer to the hard disk.
*
* You can do it manually or set auto-flushing by the second argument of
* ini::ini().
*
* @par Example of usage:
* @code
* ini inid("myini.ini");
* // make changes
* inid.flush();
* @endcode
*/
void flush (void);
/** @brief Flush changes made in the buffer to *another* file the hard disk.
*
* Using this function instead of normal flush(void), you are able to
* save the buffer to another #ini file that is not the original one.
*
* @par Example of usage:
* @code
* ini inid("myini.ini");
* // make changes
* inid.flush("myini.backup.ini");
* @endcode
*/
void flush (const char * path);
/** @brief Checks if a section exists.
*
* @param tsection - The name of the section to check, without the braces.
*
* @return #true if the section exists; #false if not.
*/
bool sectExists (const char * tsection);
/** @brief Gets the line in that a section starts.
*
* @param tsection - The name of the section to check, without the braces.
*
* @return The line in that the section starts; -1 if not-founded section.
* Keep in mind that the first line is 1, the second, 2,...
*/
int sectStart (const char * tsection);
/** @brief Gets the line in that a section ends.
*
* @param tsection - The name of the section to check, without the braces.
*
* @return The line in that the section ends; -1 if not-founded section.
* Keep in mind that the first line is 1, the second, 2,...
*/
int sectStop (const char * tsection);
/** @brief Checks if a key exists.
*
* @param tsection - The name of the section to check, without the braces.
* If the key is outside any section (if it's a #KWOS), then <em>tsection</em>
* should be #KWOS.
* @param tkey - The name of the key to check.
*
* @return #true if the key exists in the specified section; #false if not.
*/
int keyExists (const char * tsection, const char * tkey);
/** @brief Reads the value of a key as a string.
*
* @param tsection - The name of the section to read from, without the braces.
* If the key is outside any section (if it's a #KWOS), then <em>tsection</em>
* should be #KWOS.
* @param tkey - The name of the key to read its value.
* @param tval - The default string to return if cannot found the key.
*
* @return The value of the key <em>tkey</em> in section <em>tsection</em>; or
* <em>tval</em> when non-existing key.
*/
char * read (const char * tsection, const char * tkey, const char * tval);
/** @brief Reads the value of a key as an integer value.
*
* @param tsection - The name of the section to read from, without the braces.
* If the key is outside any section (if it's a #KWOS), then <em>tsection</em>
* should be #KWOS.
* @param tkey - The name of the key to read its value.
* @param tval - The default value to return if cannot found the key.
*
* @return The value of the key <em>tkey</em> in section <em>tsection</em>; or
* <em>tval</em> when non-existing key.
*/
long int readi (const char * tsection, const char * tkey, int tval);
bool delKey (const char * tsection, const char * tkey);
bool delSect (const char * tsection);
bool write (const char * tsection, const char * tkey, const char * tval);
bool write (const char * tsection, const char * tkey, int tval);
private:
unsigned long int f_size; /**< File size. */
unsigned int f_line; /**< Number of lines of the <em>ini</em> file. */
char * buffer; /**< Memory buffer to store data. Dynamimcally reallocated. */
char * f_name; /**< File name. */
bool autoflush; /**< Whether to auto-flush to hard disk or not. */
char * errord; /**< Last error stored internally by the functions of the #ini class. */
};
经过几次“测试”后，我终于发现问题出现在'f_size'变量中。为什么？不知道。但是，如果我将它打印到stdout，它会显示一个非常大的数字。这是内存分配（使用malloc）错误以及从文件读取时的后续错误（或使用memset初始化）的问题。
非常感谢帮助。和链接，参考或解释让我看到我的错误，并继续学习。
谢谢！
P.S。：我在Linux Debian中使用g ++“挤压”，amd64。
答案 0 :(得分：3)
这是一个微妙但重要的问题：
if(fd == NULL) f_size = 1; goto allocbuffer;
如果 文件存在，逻辑仍会跳转到标签allocbuffer。
要解决此问题，请使用大括号。并且为了清晰度而缩进。
if(fd == NULL)
{
f_size = 1;
goto allocbuffer;
}
跳过退出，变量未正确初始化。
答案 1 :(得分：2)
除了wallyk指出的问题之外，当ftell遇到错误时它会返回-1并将其转换为无符号长整数会导致溢出。
无论如何，don't use ftell to get a file's size。使用fstat或类似内容。
答案 2 :(得分：0)
我不会为你调试代码（这更多属于codereview.se），但这里有一些提示：
f_name = new char[strlen(path)+1];
strcpy(f_name, path);
相反：将f_name定义为std::string并执行...
f_name = path;
errord = (char*)malloc(strlen(INI_ERROR_NOT_READED) + 1);
strcpy(errord, INI_ERROR_NOT_READED);
cout << "Last error: \"" << errord << "\"." << endl;
你是否只是为了将字符串写入屏幕而动态分配内存？ 而是简单地做：
errord = INI_ERROR_NOT_READED;
cout << "Last error: \"" << errord << "\"." << endl;
同样要将整个文件读入缓冲区，还有更简单的方法（如几行代码）。请参阅https://stackoverflow.com/a/2602060/399317。
长话短说：new[]和malloc不是你的朋友，除非你自己编写容器。请改用STL容器（例如std::vector，std::string也很有用）。