C ++禁止使用可变大小的数组 [英] C++ forbids variable-size array

问题描述

我正在使用别人编写的一些现有代码，但无法编译(这里有有限的C经验，但我想学习！).

I am using some existing code that someone else has written, and I cannot get it to compile (limited C experience here but I am trying to learn!).

utilities.cc

#include "utilities.h"
FILE *open_file(char *filename, const char*extension, const char *access)
{
  char string[MAX_STR_LEN];
  FILE *strm = NULL;

  if(filename[0]=='\0')
   {
      printf("\n INPUT FILENAME (%s) > ",access);
      fgets(string,MAX_STR_LEN,stdin);
      sscanf(string,"%s",filename);
      printf(" FILE %s opened \n", filename);
   }
   int len=strlen(filename);

   if( len + strlen(extension) >= MAX_STR_LEN)
   {
      printf("\n ERROR: String Length  of %s.%s Exceeds Maximum",
              filename, extension);
      return(NULL);
   } 

   // char *filename1 = new(char[len+strlen(extension)+1]);

   const int filenameLength = len+strlen(extension)+1;
   char *filename1 = new(char[filenameLength]);

   strcpy(filename1,filename); // temp filename for appending extension

   /* check if file name has .extension    */
   /* if it does not, add .extension to it */
   int i=len-1;
   while(i > 0 && filename[i--] != '.');
   //   printf("\n Comparing %s to %s", extension, filename+i+1);
   if(strcmp(extension, filename+i+1)  )
      strcat(filename1,extension);
   if( (strm = fopen(filename1, access) ) == NULL )
   {
      printf("\n ERROR OPENING FILE %s (mode %s)", filename1,access);
   }
   delete(filename1);
   return(strm);
}

这是错误.

Compiling utilities.cc ...
src/utilities.cc: In function ‘FILE* open_file(char*, const char*, const char*)’:
src/utilities.cc:251: error: ISO C++ forbids variable-size array
gmake: *** [/home/landon/geant4/work/tmp/Linux-g++/exampleN01/utilities.o] Error 1

第251行的错误是

char *filename1 = new(char[filenameLength]);

如果您需要任何其他信息，请告诉我.

If you need any additional information let me know please.

推荐答案

该错误是正确的.C ++中禁止使用VLA(可变大小数组).这是一个VLA:

The error is correct. VLA(variable size arrays) are forbidden in C++. This is a VLA:

char filename1char[filenameLength];

您可能是这个意思:

char *filename1 = new char[filenameLength];

这不是VLA，而是在堆上分配的 char 数组.请注意，您应该使用运算符 delete [] :

Which is not a VLA, but an array of chars allocated on the heap. Note that you should delete this pointer using operator delete[]:

delete[] filename1;

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