Pointers C-错误为；free（）：无效的下一个大小（正常）"；

我就是找不到造成这个问题的原因

MYSQL *startup(unsigned char *path_to_file, int size_of_path) {
MYSQL *con;
bool path_is_file = false;
bool path_is_directory = false;
FILE *startup_file;
int i;
unsigned char buffer[LINEBUFFERSIZE];
unsigned char string[LINEBUFFERSIZE];
unsigned char c;

//Allocate memory for the new file path
unsigned char *path;
path = (unsigned char *) malloc(size_of_path);
if(path == NULL)
    error("Could not allocate memory for path to file.\nIn startup()\n");

//Check if startup file exists or if it is a directory
//Bug is somewehre here!!!!
struct stat s;
printf("%s", path_to_file);
if(stat(path_to_file, &s) == 0) {
    if(s.st_mode & S_IFDIR) {
        //It's a directory
        path_is_directory = true;
        //Add the standard startup file name to the directory
        path = (unsigned char *) realloc(path, size_of_path + sizeof(STARTUP_FILE));
        if(path == NULL)
            error("Could not reallocate memory for variable path.\nIn startup()\n");
        //Put the strings together
        sprintf(path, "%s/%s", path_to_file, STARTUP_FILE);
    }
    else if(s.st_mode & S_IFREG) {
        //It's a file
        path_is_file = true;
        path = path_to_file;
    }//End else if
    else //Someting else. abort
        error("Given file is neither file or directory.\nIn startup()\n");
}
else //Error
    error("Error in looking up type of path.\nIn startup()\n");;


//Check if the startup file exists
fprintf(stderr, "%s\n", path);
if((startup_file = fopen(path, "r")) == NULL) {
    //File does not exist, create a basics one for the user to modify
    if((startup_file = fopen(path, "w+")) == NULL)
        error("Could not create the startup file.\n");
    //Write the standard text to the new file, so the user can modify it
    //sizeof(STARTUP_FILE_TEXT)-1 as gedit cries if there is a terminator at the end
    fwrite(STARTUP_FILE_TEXT, sizeof(STARTUP_FILE_TEXT[0]), sizeof(STARTUP_FILE_TEXT)-1, startup_file);
}//End outer if


//Read from the startup file and find out which tables and database are needed and may have to be created
//While loop will run although if file was just created, fix it
section current;
while(fgets(buffer, sizeof(buffer), startup_file) != NULL) {
    if(strcmp(buffer, "[DATABASES]")) {
        //Every line now should contain the name of dbs, until new section
        current = DATABASES;
    }
    else if(strcmp(buffer, "[TABLES]")) {
        //Every line now should contain the name of dbs, until new section
        current = TABLES;
    }
    else {
        //Read the lines and create the table or database
        //Ignore everything behind #
        //Just numbers and letters are allowed
        //Read one line and save it into buffer
        //What happens, if the line exceeds buffer length and is split into to?
        //Process every character, but do not exceed the buffers limit (also save one for the '\0' termiantor)
        for(i = 0; i < (sizeof(buffer)-1); i++) {
            //Allowed characters are: A-Z, a-z, 0-9, dash, underscore and space
            //Read until '\n' or '#' or if not allowed characters are used print error and do not use it
            c = buffer[i];
            if(isalnum(c) || (c == '-') || (c == '_') || (c == ' '))  {
                //Correct
                string[i] = c;
            }//End if
            else if(c == '\n' || c == '\0') {
                //End of line or end of string, not checking for EOF as fgets already does it \
                and it would requried the int data type
                break;
            }//End else if
            else {
                //Wrong, stop
                printf("Wrong character used in setup file.\nWrong characters was: %c\n", c);
                break;
            }//End else
        }//End for
        //Add terminator at the end
        string[i] = '\0';
        //Create table or database
        switch(current) {
            case DATABASES:
                create_db(string, sizeof(string));
                break;
            case TABLES:
                break;
            default:
                break;
        }//End switch

    }
}//End while

//Create db and then open the database as a specific user
//create_db();
con = open_db("user1", "passwd", "Vocables");

//Clean up
fclose(startup_file);
free(path);
return con;
}

在gdb中执行单行时，您会在错误发生之前缩短：

    26              path_is_directory = true;
(gdb) n
28              path = (unsigned char *) realloc(path, size_of_path + sizeof(STARTUP_FILE));
(gdb) n
29              if(path == NULL)
(gdb) n
32              sprintf(path, "%s/%s", path_to_file, STARTUP_FILE);
(gdb) n
51      fprintf(stderr, "%s\n", path);
(gdb) n
/home/linux/Cloud/Decrypted/Porifera-Server//startup.txt
52      if((startup_file = fopen(path, "r")) == NULL) {
(gdb) n

当我在第52行之后执行下一行时，问题就出现了

使用“valgrind--leak check=yes./Porifera Server 8080~/Cloud/Decrypted/Porifera Server”，它实际上运行正常。但却有一大堆“错误”：

---

我就是找不到它；其他出现类似错误的人要么在

fopen

函数的文件路径中有“\n”，要么没有初始化ptr，但试图释放它。自上次运行以来，我没有接触过任何ptr自由功能，目前我还没有找到导致此问题的ptr。

当遇到错误时，请从1开始。第一，它可能是以下错误的原因

MYSQL *startup(unsigned char *path_to_file, int size_of_path) {
MYSQL *con;
bool path_is_file = false;
bool path_is_directory = false;
FILE *startup_file;
int i;
unsigned char buffer[LINEBUFFERSIZE];
unsigned char string[LINEBUFFERSIZE];
unsigned char c;

//Allocate memory for the new file path
unsigned char *path;
path = (unsigned char *) malloc(size_of_path);
if(path == NULL)
    error("Could not allocate memory for path to file.\nIn startup()\n");

//Check if startup file exists or if it is a directory
//Bug is somewehre here!!!!
struct stat s;
printf("%s", path_to_file);
if(stat(path_to_file, &s) == 0) {
    if(s.st_mode & S_IFDIR) {
        //It's a directory
        path_is_directory = true;
        //Add the standard startup file name to the directory
        path = (unsigned char *) realloc(path, size_of_path + sizeof(STARTUP_FILE));
        if(path == NULL)
            error("Could not reallocate memory for variable path.\nIn startup()\n");
        //Put the strings together
        sprintf(path, "%s/%s", path_to_file, STARTUP_FILE);
    }
    else if(s.st_mode & S_IFREG) {
        //It's a file
        path_is_file = true;
        path = path_to_file;
    }//End else if
    else //Someting else. abort
        error("Given file is neither file or directory.\nIn startup()\n");
}
else //Error
    error("Error in looking up type of path.\nIn startup()\n");;


//Check if the startup file exists
fprintf(stderr, "%s\n", path);
if((startup_file = fopen(path, "r")) == NULL) {
    //File does not exist, create a basics one for the user to modify
    if((startup_file = fopen(path, "w+")) == NULL)
        error("Could not create the startup file.\n");
    //Write the standard text to the new file, so the user can modify it
    //sizeof(STARTUP_FILE_TEXT)-1 as gedit cries if there is a terminator at the end
    fwrite(STARTUP_FILE_TEXT, sizeof(STARTUP_FILE_TEXT[0]), sizeof(STARTUP_FILE_TEXT)-1, startup_file);
}//End outer if


//Read from the startup file and find out which tables and database are needed and may have to be created
//While loop will run although if file was just created, fix it
section current;
while(fgets(buffer, sizeof(buffer), startup_file) != NULL) {
    if(strcmp(buffer, "[DATABASES]")) {
        //Every line now should contain the name of dbs, until new section
        current = DATABASES;
    }
    else if(strcmp(buffer, "[TABLES]")) {
        //Every line now should contain the name of dbs, until new section
        current = TABLES;
    }
    else {
        //Read the lines and create the table or database
        //Ignore everything behind #
        //Just numbers and letters are allowed
        //Read one line and save it into buffer
        //What happens, if the line exceeds buffer length and is split into to?
        //Process every character, but do not exceed the buffers limit (also save one for the '\0' termiantor)
        for(i = 0; i < (sizeof(buffer)-1); i++) {
            //Allowed characters are: A-Z, a-z, 0-9, dash, underscore and space
            //Read until '\n' or '#' or if not allowed characters are used print error and do not use it
            c = buffer[i];
            if(isalnum(c) || (c == '-') || (c == '_') || (c == ' '))  {
                //Correct
                string[i] = c;
            }//End if
            else if(c == '\n' || c == '\0') {
                //End of line or end of string, not checking for EOF as fgets already does it \
                and it would requried the int data type
                break;
            }//End else if
            else {
                //Wrong, stop
                printf("Wrong character used in setup file.\nWrong characters was: %c\n", c);
                break;
            }//End else
        }//End for
        //Add terminator at the end
        string[i] = '\0';
        //Create table or database
        switch(current) {
            case DATABASES:
                create_db(string, sizeof(string));
                break;
            case TABLES:
                break;
            default:
                break;
        }//End switch

    }
}//End while

//Create db and then open the database as a specific user
//create_db();
con = open_db("user1", "passwd", "Vocables");

//Clean up
fclose(startup_file);
free(path);
return con;
}

==17917== Invalid write of size 8
==17917==    at 0x5E53E04: __GI_mempcpy (in /usr/lib/libc-2.21.so)
==17917==    by 0x5E44BDD: _IO_default_xsputn (in /usr/lib/libc-2.21.so)
==17917==    by 0x5E18C61: vfprintf (in /usr/lib/libc-2.21.so)
==17917==    by 0x5E3AC2A: vsprintf (in /usr/lib/libc-2.21.so)
==17917==    by 0x5E1F266: sprintf (in /usr/lib/libc-2.21.so)
==17917==    by 0x401647: startup (server_func.c:32)
==17917==    by 0x4012BB: main (server.c:23)
==17917==  Address 0x6c8709e is 14 bytes inside a block of size 20 alloc'd
==17917==    at 0x4C2C29E: realloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==17917==    by 0x40160B: startup (server_func.c:28)
==17917==    by 0x4012BB: main (server.c:23)

在这个堆栈跟踪中，interesting片段是程序的代码，因为我们可以假设运行时/标准库中的代码可以工作

Valgrind在这里告诉您两件事：

在文件服务器_func.c第32行的启动函数中，您正在访问不应该访问的内存（大小为8的无效写入）

您正在访问的内存超过了您在server_func.c第28行分配的20个字节的缓冲区14个字节

第28行：

path=（unsigned char*）realloc（路径，路径的大小+sizeof（启动文件））

第32行：
sprintf（路径，“%s/%s”，路径到文件，启动文件）

所以在第28行中，您没有为“/”分隔符分配空间，也可能没有为nul终止符分配空间

您还需要确保路径的
size\u
是正确的，并且
sizeof（STARTUP\u FILE）
为您提供了正确的大小，如果
STARTUP\u FILE
是一个字符数组，它将提供正确的大小，但是如果它是一个字符指针，它将是错误的。也许您需要使用strlen（启动文件）

假设
size\u of_path
是正确的，您可能需要将缓冲区大小计算为
size\u of_path+strlen（启动文件）+2
这表示您使用realloc（）创建的缓冲区太小，因此下面的
sprintf（路径，“%s/%s”，路径到启动文件，启动文件）可能会破坏内存。但是，我们不知道sizeof（STARTUP_FILE）或size_of_path是什么，也不知道它们是否正确-也许STARTUP_FILE是一个char*但您假设它是一个数组。不过，您需要为“/”和nul终止符分配空间。是的，您是对的，尽管我确信分配了足够的内存。但这解决了问题。您能告诉我您是如何发现的吗？或者引用gdb或valgrind输出的行，以便下次我知道，因为我仍然是初学者。：-）我使用了sizeof（argv[2]），但它返回的长度绝对错误。有没有办法找出命令行参数的大小？是的，strlen（argv[2]）给出了长度，不包括nul终止符。H，感谢您的解释：-）当我使用sizeof（argv[2]）来找出它时，路径的大小是不正确的，但它是一个字符指针，所以我将它改为strlen（argv[2]）：-）
==17917== Invalid write of size 8
==17917==    at 0x5E53E04: __GI_mempcpy (in /usr/lib/libc-2.21.so)
==17917==    by 0x5E44BDD: _IO_default_xsputn (in /usr/lib/libc-2.21.so)
==17917==    by 0x5E18C61: vfprintf (in /usr/lib/libc-2.21.so)
==17917==    by 0x5E3AC2A: vsprintf (in /usr/lib/libc-2.21.so)
==17917==    by 0x5E1F266: sprintf (in /usr/lib/libc-2.21.so)
==17917==    by 0x401647: startup (server_func.c:32)
==17917==    by 0x4012BB: main (server.c:23)
==17917==  Address 0x6c8709e is 14 bytes inside a block of size 20 alloc'd
==17917==    at 0x4C2C29E: realloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==17917==    by 0x40160B: startup (server_func.c:28)
==17917==    by 0x4012BB: main (server.c:23)