C ++ - 已弃用从字符串常量到'char *'的转换 [英] C++ - deprecated conversion from string constant to ‘char*’

问题描述

可能重复：

从字符串常量到字符串常量的过时转换错误

我试图运行旧的C ++代码今天（这个代码走在2004年:)。但现在我得到了这个错误消息：

  make [1]：输入目录`/home/thehost/Plocha/lpic-1.3 .1 / lpic / src'
 source ='error.C'object ='error.o'libtool = no \ 
 depfile ='。deps / error.Po'tmpdepfile ='。deps / error.TPo'\ 
 depmode = gcc3 / bin / bash ../../config/depcomp \ 
 g ++ -DHAVE_CONFIG_H -I。 -一世。 -I ../ .. -g -O2 -Wno-deprecated -g -O2 -c -o error.o`test -f'error.C'|| echo'./'`error.C 
 error.C：在构造函数'error_handler :: error_handler（const char *，char *）'：
 error.C：49：7：error：'cerr '未在此范围中声明
 error.C：58：11：warning：不推荐从字符串常量转换为'char *'[-Wwrite- strings] 
 error.C：58：11：warning ：不推荐从字符串常量转换为'char *'[-Wwrite- strings] 
 error.C：58：11：warning：不推荐从字符串常量转换为'char *'[-Wwrite- strings] 
 error.C：58：11：warning：从字符串常量转换为'char *'[-Wwrite- strings] 
 make [1]：*** [error.o]错误1 
 make [1]：离开目录`/home/thehost/Plocha/lpic-1.3.1/lpic/src'
 make：*** [all-recursive]错误1 
  

error.C文件的来源：

  ... 
 #include< error.h> 
 
 int error_handler :: error_number = 0; 
 int error_handler :: message_number = 0; 
 int error_handler :: debug_number = 0; 
 int error_handler :: Q_debug = 1; 
 int error_handler :: object_number = 0; 
 int error_handler :: tab = 33; 
 
 error_handler :: error_handler（const char * name，char * error_file_name）
 {
 errname = new char [filename_size]; 
 strcpy（errname，error_file_name）; 
 
 errfile.open（errname，ios :: app）; 
 
 if（！errfile）
 {
 cerr<< error_handler：无法打开错误文件< errname<< endl; 
 exit（1）; 
} 
 
 errfile.close（）; 
 
 my_name = name; 
 object_number ++; 
 
 debug（）; 
} 
 
 
 void error_handler :: error（char * s1，char * s2，char * s3，char * s4）
 {
 error_number ++; 
 
 errfile.open（errname，ios :: app）; 
 errfile.setf（ios :: left）; 
 
 errfile<< FAILURE：<< setw（tab）<< my_name<< < s1<< ''<< s2 
<< s3 < s4<< endl; 
 
 errfile.close（）; 
 
 exit（1）; 
} 
 ... 
  

error.h文件的来源：

  ... 
 using namespace std; 
 
 class error_handler {
 static int error_number; 
 static int message_number; 
 static int Q_debug; 
 static int debug_number; 
 static int object_number; 
 const char * my_name; 
 
 char * errname; 
 
 ofstream errfile; 
 static int tab; 
 public：
 error_handler（const char *，char * error_file_name）; 
 
 
 void错误（char * s1，char * s2 =，
 char * s3 =，char * s4 = 
 void error（char * s1，double d2，
 char * s3 =，char * s4 =）; 
 
 void message（char * m1，
 char * m2 =，char * m3 =，char * m4 = 
 void message（char * m1，double m2，
 char * m3 =，char * m4 =）; 
 void message（char * m1，double m2，char * m3，double m4）; 
 void message（char * m1，double m2，char * m3，double m4，
 char * m5，double m6，char * m7，double m8） 
 void message（char * m1，double m2，double m3，double m4，double m5）; 
 void message（char * m1，double m2，double m3，double m4）; 
 void message（char * m1，double m2，char * m3，double m4，char * m5，double m6）; 
 void message（char * s1，double d2，double d3）; 
 void message（char * s1，char * s2，double d3）; 
 
 void debug（char * m1，
 char * m2 =，char * m3 =，char * m4 = 
 void debug（char * m1，double m2，
 char * m3 =，char * m4 =）; 
 void debug（char * m1，double m2，char * m3，double m4）; 
 void debug（char * m1，double m2，char * m3，double m4，char * m5，double m6）; 
}; 
 
 #endif 
  

你有什么想法如何解决？如果是，请把它清楚地写下来（我是新手...）。
谢谢！

解决方案

我认为您的警告来自此代码：

  void message（char * m1，
 char * m2 =，char * m3 =，char * m4 =问题是C ++中的字符串文字可以被当作 char * 
 / code> s，但这是非常不安全的。写入由字符串字面量定义的数组会导致未定义行为（导致安全漏洞，程序崩溃等事件的类型），但是一个常规的ol < c> char * 指针将允许你做这种类型的写。由于这个原因，这是强烈建议你使所有 char * ，将指向一个C风格的字符串，而不是 const char *  s，以便编译器可以检查以确保您不会尝试写入它们。在这种情况下，你的代码最好写成
  void message（char * m1，
 const char * m2 =，const char * m3 =，const char * m4 =）; 
  
但是，由于您使用的是C ++，很多只是使用 std :: string ：
 ：string m1，
 std :: string m2 =，std :: string m3 =，std :: string m4 =）; 
  
这完全避免了这个问题，因为C ++  std :: string 类型在其参数中正确地具有 const char * ，并且创建了字符串的深层副本，因此如果您尝试变异字符串， 
 
 
 
希望这有助于！
 

  
Possible Duplicate:

  Deprecated conversion from string constant to char * error  
I tried to run old C++ code today (this code gone right in 2004 :). But now I got this error message:
make[1]: Entering directory `/home/thehost/Plocha/lpic-1.3.1/lpic/src'
source='error.C' object='error.o' libtool=no \
depfile='.deps/error.Po' tmpdepfile='.deps/error.TPo' \
depmode=gcc3 /bin/bash ../../config/depcomp \
g++ -DHAVE_CONFIG_H -I. -I. -I../..    -g -O2 -Wno-deprecated  -g -O2 -c -o error.o `test -f 'error.C' || echo './'`error.C
error.C: In constructor ‘error_handler::error_handler(const char*, char*)’:
error.C:49:7: error: ‘cerr’ was not declared in this scope
error.C:58:11: warning: deprecated conversion from string constant to ‘char*’ [-Wwrite-    strings]
error.C:58:11: warning: deprecated conversion from string constant to ‘char*’ [-Wwrite-    strings]
error.C:58:11: warning: deprecated conversion from string constant to ‘char*’ [-Wwrite-    strings]
error.C:58:11: warning: deprecated conversion from string constant to ‘char*’ [-Wwrite-    strings]
make[1]: *** [error.o] Error 1
make[1]: Leaving directory `/home/thehost/Plocha/lpic-1.3.1/lpic/src'
make: *** [all-recursive] Error 1
Source of "error.C" file:
...
#include <error.h>

int error_handler::error_number   = 0;
int error_handler::message_number = 0;
int error_handler::debug_number   = 0;
int error_handler::Q_debug        = 1;
int error_handler::object_number  = 0;
int error_handler::tab            = 33;  

error_handler::error_handler(const char *name, char *error_file_name)
{
  errname = new char [filename_size];
  strcpy(errname,error_file_name);

  errfile.open(errname,ios::app);

  if (!errfile)
    {
      cerr << "error_handler: cannot open error file " << errname << endl;
      exit(1);
    }

  errfile.close();

  my_name = name;
  object_number++;

  debug("");
}


void error_handler::error(char* s1, char* s2, char *s3, char *s4)
{
  error_number++ ;

  errfile.open(errname,ios::app);
  errfile.setf(ios::left);

  errfile << "FAILURE: " << setw(tab) << my_name << "       " << s1 << ' ' << s2
    << s3 << s4 << endl;

  errfile.close();

exit(1);
}
...
And source of "error.h" file:
...
using namespace std;

class error_handler {
static int error_number;
static int message_number;
static int Q_debug;
static int debug_number;
static int object_number;
const char *my_name;

char       *errname;

ofstream   errfile;
static int tab;
public:
error_handler(const char *, char *error_file_name);


void error(char* s1,    char*  s2="",
       char* s3="", char*  s4="");
void error(char* s1,    double d2,
       char* s3="", char*  s4="");

void message(char* m1,
     char* m2="", char*  m3="", char* m4="");
void message(char* m1,    double m2,
     char* m3="", char*  m4="");
void message(char* m1,    double m2,    char* m3, double m4);
void message(char* m1,    double m2,    char* m3, double m4,
     char* m5,    double m6,    char* m7, double m8);
void message(char* m1, double m2, double m3, double m4, double m5 );
void message(char* m1, double m2, double m3, double m4 );
void message(char* m1, double m2, char* m3,  double m4, char* m5, double m6);
void message(char *s1, double d2, double d3);
void message(char *s1, char *s2, double d3);

void debug(char* m1,
       char* m2="", char*  m3="", char* m4="");
void debug(char* m1,    double m2,
       char* m3="", char*  m4="");
void debug(char* m1   , double m2,    char* m3, double m4);
void debug(char* m1   , double m2,    char* m3, double m4, char* m5, double m6);
};

#endif
Have you any idea how I could fix it? If yes, please write it down clearly (I am newbie...).
Thank you!
解决方案
I think that your warnings are coming from this code:
void message(char* m1,
     char* m2="", char*  m3="", char* m4="");
The issue is that string literals in C++ can be treated as char*s, but it's very unsafe to do so.  Writing to an array defined by a string literal results in Undefined Behavior (the sort of thing that causes security holes, program crashes, etc.), but a regular ol' char* pointer would allow you to do this sort of write.  For this reason, it is strongly suggested that you make all char*s that would point to a C-style string instead be const char*s so that the compiler can check to make sure that you aren't try to write to them.  In this case, your code would be better written as
void message(char* m1,
     const char* m2="", const char*  m3="", const char* m4="");
However, since you're using C++, a much better idea is just to use std::string:
void message(std::string m1,
     std::string m2="", std::string m3="", std::string m4="");
This completely avoids the issue, because the C++ std::string type correctly has const char*s in its arguments and makes a deep-copy of the string, so if you try to mutate the string it's guaranteed that you're not going to be trashing the original array of characters.

Hope this helps!

                        
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