【发布时间】：2012-01-27 16:13:45
【问题描述】：
几周前，我第一次使用（我不习惯使用它们）floats，doubles，我在比较时遇到了一些问题操作数。我在尝试为这些类型分配值时也遇到了问题，但我也解决了它......
今天，我正在用 C++ 制作一个库，但我发现了一个错误……嗯……奇怪？还是只是我的愚蠢想法？
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 ini 库已经创建，并且比我的要好得多。但是我开始从 C 学习 C++，我想练习一些有趣和有用的东西。错过了类声明，不知道有没有必要贴在这里，不过这里是：
/** @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”，我终于发现问题出在“f_size”变量上。为什么？不知道。但是，如果我将它打印到标准输出，它会显示一个非常大的数字。这就是内存分配（使用 malloc）错误以及从文件读取（或使用 memset 初始化）时的后续错误的问题。
非常感谢您的帮助。以及链接、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“挤压”中使用 g++，amd64。
【问题讨论】：
-
顺便说一句
strlen和new char[]?甚至malloc？你还在用 C 语言思考，使用std::string和繁荣 -
但是我看到的很多函数“仍然”使用 const char* 和 char*... 我需要 realloc 为缓冲区动态重新分配内存。
-
如果您不编写容器类，为什么需要为缓冲区动态重新分配内存？
-
ftell返回一个 signed long int。由于ftell在错误时返回-1，因此您的转换可能非常显着。+1在这条线上也很可疑。goto allocbuffer;在 C++ 中确实应该避免使用。这在 C 中是可以的（虽然不确定是否在这种情况下），但是在 C++ 中要正确要困难得多。 （因此，您仍然在 C 方面考虑太多 - 用一段更简单的代码很多缩小您的问题范围，您可能会得到更好的建议。） -
如果您使用
std::string和std::ifstream，则不需要 realloc。我建议你学习使用它们，因为它会让你的内存管理更容易。
标签： c++ g++ unsigned-integer unsigned-long-long-int