C++ - 不推荐将字符串常量转换为'char*'

Question

可能重复:
从字符串常量到char*错误的过时转换

我今天试图运行旧的C++代码(这个代码在2004年正确:).但现在我收到此错误消息:

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

"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: 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);
}
...

和"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 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

你知道我怎么解决它吗？如果是,请清楚地写下来(我是新手......).谢谢!

Answer 1

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视为char*s,但这样做是非常不安全的.写入由字符串文字定义的数组会导致未定义的行为(导致安全漏洞,程序崩溃等的事情),但是常规的ol' char*指针将允许您执行此类写操作.出于这个原因,强烈建议您将所有char*指向C风格字符串的const char*s 改为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,您的代码将更好地编写为

void message(char* m1,
     const char* m2="", const char*  m3="", const char* m4="");

但是,既然你正在使用C++,那么更好的想法就是使用std::string:

void message(std::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const char*在其参数中正确地有s并且是字符串的深层副本,因此如果你试图改变字符串,那么它可以保证你不会破坏原始的字符数组.

希望这可以帮助!

Answer 2

你有几个选择:

• 修复你的代码,以便字符串文字(例如"foo")永远不会被隐式转换为char*.他们应该const char*.

• 将编译器命令行更改为include -Wno-write-strings.这是-Wwrite-strings错误消息的一部分暗示.

我更喜欢第一种选择.