インスタンスをロードするときのcpp開発者のEXC_BAD_ACCESフォールト

Question

最近、私はC++の学習を始めました。私はObjective-Cでプログラミングすることに慣れているので、多分私はいくつかのことを間違っています。私はgdbセッションのトランスクリプトを作成しました：

Script started on Sat Jan 15 17:47:24 2011 
bash-3.2$ gdb sscm 
GNU gdb 6.3.50-20050815 (Apple version gdb-1510) (Wed Sep 22 02:45:02 UTC 2010) 
Copyright 2004 Free Software Foundation, Inc. 
GDB is free software, covered by the GNU General Public License, and you are 
welcome to change it and/or distribute copies of it under certain conditions. 
Type "show copying" to see the conditions. 
There is absolutely no warranty for GDB. Type "show warranty" for details. 
This GDB was configured as "x86_64-apple-darwin"...Reading symbols for shared libraries ... done 

(gdb) break ServerOptions::ServerOptions 
[0] cancel 
[1] all 
[2] ServerOptions::ServerOptions(int, char const**) at ServerOptions.cpp:33 
[3] ServerOptions::ServerOptions(int, char const**) at ServerOptions.cpp:33 
> 3 
Breakpoint 1 at 0x7595: file ServerOptions.cpp, line 33. 
(gdb) list 
9 
10 #include <iostream> 
11 
12 #include "Logger.h" 
13 #include "ServerOptions.h" 
14 
15 
16 int main(int argc, const char **argv) { 
17 using namespace std; 
18 ServerOptions options(argc, argv); 
(gdb) run 
Starting program: /Users/ief2/Desktop/SSCM-1.0.0.9/server/sscmd 
Reading symbols for shared libraries ++. done 

Breakpoint 1, ServerOptions::ServerOptions (this=0xbffff7a8, argc=1, argv=0xbffff7f0) at ServerOptions.cpp:33 
33 ServerOptions::ServerOptions(int argc, const char **argv) 
(gdb) s 
36 bool noErrorsEncountered = true; 
(gdb) list 
31 is a fatal error. 
32 */ 
33 ServerOptions::ServerOptions(int argc, const char **argv) 
34 { 
35 /* setup default values */ 
36 bool noErrorsEncountered = true; 
37 int isDaemon = true; 
38 int displayHelp = false; 
39 int port = DEFAULT_BIND_PORT; 
40 std::string rootFolder = ""; 
(gdb) s 
37 int isDaemon = true; 
(gdb) s 
38 int displayHelp = false; 
(gdb) s 
39 int port = DEFAULT_BIND_PORT; 
(gdb) 
40 std::string rootFolder = ""; 
(gdb) list 
35 /* setup default values */ 
36 bool noErrorsEncountered = true; 
37 int isDaemon = true; 
38 int displayHelp = false; 
39 int port = DEFAULT_BIND_PORT; 
40 std::string rootFolder = ""; 
41 int isSilent = 0; 
42 
43 Logger logger = Logger::sharedLogger(); 
44 
(gdb) 
45 /* Process the configuration file */ 
46 { 
47 int status; 
48 std::string anArgument; 
49 KeyFile file(DEFAULT_CONFIGURATION_FILE, 
50  &status); 
51 
52 if(status != 0 && status != ENOENT) { 
53 std::stringstream strstr; 
54 strstr << 
(gdb) lists[Klists[K 
41 int isSilent = 0; 
(gdb) 
43 Logger logger = Logger::sharedLogger(); 
(gdb) 
Logger::sharedLogger() at Logger.cpp:28 
28 if(logger == NULL) { 
(gdb) list 
23 } 
24 
25 Logger& Logger::sharedLogger(void) { 
26 static Logger *logger = NULL; 
27 
28 if(logger == NULL) { 
29 new Logger(""); 
30 } 
31 
32 return *logger; 
(gdb) s 
29 new Logger(""); 
(gdb) 
Logger::Logger (this=0x100160, fullPath=@0xbffff568) at Logger.cpp:16 
16 Logger::Logger(std::string fullPath) { 
(gdb) list 
11 
12 #pragma mark - 
13 #pragma mark Public Implementation 
14 
15 #pragma mark Constructors and Destructors 
16 Logger::Logger(std::string fullPath) { 
17 _filename = fullPath; 
18 _isSilent = false; 
19 } 
20 
(gdb) s 
17 _filename = fullPath; 
(gdb) 
18 _isSilent = false; 
(gdb) 
19 } 
(gdb) 
Logger::sharedLogger() at Logger.cpp:32 
32 return *logger; 
(gdb) 
33 } 
(gdb) 
Logger::Logger (this=0xbffff6ec) at Logger.h:21 
21 class Logger { 
(gdb) llist ist 
16 #include <cerrno> 
17 #include <cstring> 
18 
19 #pragma mark - 
20 #pragma mark Private Interface 
21 class Logger { 
22 private: 
23 std::string _filename; 
24 bool _isSilent; 
25 
(gdb) 
26 public: 
27 #pragma mark Constructors and Destructors 
28 Logger(std::string fullPath); 
29 ~Logger(void); 
30 static Logger& sharedLogger(void); 
31 
32 #pragma mark Getters and Setters 
33 std::string getFilename(void) const; 
34 void setFilename(std::string newF); 
35 
(gdb) s 

Program received signal EXC_BAD_ACCESS, Could not access memory. 
Reason: KERN_PROTECTION_FAILURE at address: 0x00000000 
0x980f7b33 in std::basic_string<char, std::char_traits<char>, std::allocator<char> >::basic_string() 
(gdb) ki 
Kill the program being debugged? (y or n) y 
(gdb) q 
bash-3.2$ exit 
exit 

Script done on Sat Jan 15 17:48:59 2011 

なぜこのエラーが発生しているのですか？より多くのコードが必要な場合は、私は確かにそれを投稿します！

あなたはライン29上のライン32上のNULLポインタを参照解除され、事前にIEF2

Answer 1

をありがとう、あなたは新しいLoggerを作成しますが、loggerに割り当てることはありません。したがって、sharedLoggerから返すと、はまだNULLであり、アクセス違反が発生します。 29行目を

logger = new Logger(""); 

に変更してください。

Answer 2

私は、これが問題だと思う：

Logger& Logger::sharedLogger(void) { 
    static Logger *logger = NULL; 

    if(logger == NULL) { 
     new Logger(""); 
    } 

    return *logger; 
} 

あなたはSingleton patternを目指している場合 - すなわち、静的logger変数にその新しく作成されたインスタンスのアドレスを割り当てる：

 logger = new Logger("");