C：定义一个long作为返回类型函数的数组

Question

in C# I would just do:

private long[] myMethodName()
{
    //etc
}

What is the equivalent in C?

This gives an error:

long[] readSeqFile(char *fileName)

Answer 1

long *readSeqFile(char *filename);

You might want to make filename const:

long *readFileName(const char *const filename);

UPDATE: while this answers the original question, it's not very good C practise. If, as the poster says, he wants to read a list of integers from a file and get it back as an array of long, then the prototype is probably going to look something like this:

int readSeqFile(const char *const filename,long **longArray,size_t *const len);

and the implementation (in sketch form):

#include <stdio.h>
#include <stdlib.h>

const size_t longArrayChunkSize=100;

int readSeqFile(const char *const filename,long **longArray, size_t *const len)
{
   FILE *fp;
   size_t nInts=0,curBufferLen;
   long tmp;

   fp=fopen(filename,"r");
   if(fp==NULL)
      return -1;

   *longArray=malloc(longArrayChunkSize*sizeof(long));
   if(*longArray==NULL)
      return -1;

   curBufferLen=longArrayChunkSize;

   // let's assume file is a list of integers, one per line
   while(read from file and !feof())
       {
       (scan line into tmp)
       longArray[nInts++]=tmp;
       if(nInts==curBufferLen)
          (realloc *longArray by longArrayChunkSize, increase curBufferLen)
       }

   *len=nInts;

   fclose(fp);

   return 0;
}

Call it like this: result=readSeqFile(filename,&longArray,&arrayLen); longArray is of type long* and it is the caller's responsibility to free it afterwards. The result is zero on success and -1 on error.

This is where you win with C++ and STL classes like vector<long> since you can just push_back() each long as it comes out of the file without having to worry about memeory management.

Answer 2

Typically for C you would pass a pointer and length

// returns number of elements written
size_t myMethodName(long* dest, size_t len)
{
    //etc
}

Answer 3

Nevermind.. I got it:

long *readSeqFile(char *fileName)

Thanks anyway

Answer 4

In C, functions cannot return array types; they can return pointers to arrays, such as

long (*readSeqFile(char *filename))[N]
{
  ...
}

the downside being that N must be a compile time constant if you're using a C89 or earlier compiler, or a C2011 compiler that doesn't support variable length arrays. You probably don't want to go this route if you don't know how big the array is supposed to be ahead of time.