Question

问题：在哪种情况下（除了实际到达文件末尾）是C-stdlib返回EOF的getchar函数？

我的目标是将整个文件读入内存缓冲区。所以我想我打开一个文件，检查它的大小，为它分配一个缓冲区，如果有效，那么在for循环中读取文件的每个char到分配的内存中：

int main ( int argc , char *argv[] )
{
    long cpos,epos,l;   
    int i;
    char *p;

    if ( argc == 1)
    {
        printf ("FAIL : no file specified\n");
        exit (-255);
    }
    else
    {
        myMdfFile = fopen ( argv[1] , "r" );
        if (myMdfFile == NULL)
        {
            printf ("FAIL : cannot open file %s\n" , argv[1]);
            exit (-254);            
        }
        else
        {
            fseek( myMdfFile , 0 , SEEK_END );
            epos = ftell(myMdfFile);
            fseek( myMdfFile , 0 , SEEK_SET );  

            pAll = malloc( epos );

            if ( pAll )
            {
                p = (char *)pAll;

                for (l=0;l<epos;l++)
                {
                    i = fgetc(myMdfFile);
                    if ( i == EOF )
                    {
                        if ( l == epos-1 )
                        {
                            printf ("NOTE : %u bytes read \n" , l);
                        }
                        else
                        {
                            printf ("NOTE : file has error errno : %d [0x%02x]\n", errno , errno );
                            cpos = ftell(myMdfFile);
                            printf ("pos is at 0x%08x" , cpos);
                            printf (" ... ...  EOF is at 0x%08x \n" , epos );
                            printf ("Why is the file giving me at %d EOF actually %d bytes before real EOF\n" , l , epos - cpos );
                            exit (-248);                
                        }
                    }   
                    else
                    {
                        *p = i;
                        p++;
                    }
                }
                free (pAll);    
            }
            else
            {
                printf ("FAIL : cannot allocate %u bytes of memory \n" , epos);
                exit (-255);
            }
        }
    }
    return 0;
}

但是getchar并没有让我知道文件中的内容。它自发地决定返回EOF：

D:\rampage\mdfun>mdfun.exe 3064213.mdf
NOTE : file has error errno : 0 [0x00]
pos is at 0x00002000 ... ... EOF is at 0x000b571b
Why is the file giving me at 7136 EOF actually 735003 bytes before real EOF

第7137个字节（l从0开始）是0x00（另见：binary file 3064213.mdf contents at position of l at exit）。在文件中的位置0x2000也是普通的0x00。（另见：binary file 3064213.mdf contents at position of cpos at exit）。

顺便说一下为什么getchar调用次数（在l = 7136中）和streampointer位置（cpos = 0x2000 = 8192）之间存在如此显着的偏差？ getchar不应仅通过sizeof（char）来增加每个成功检索到的字符的streampointer位置吗？

我在win7 dos shell中使用mingw：

Reading specs from C:/Programme/Razorcat/MSYS_MinGW/MinGW/bin/../lib/gcc/mingw32/3.4.5/specs
Configured with: ../gcc-3.4.5-20060117-3/configure --with-gcc --with-gnu-ld --with-gnu-as --host=mingw32 --target=mingw32 --prefix=/mingw --enable-threads --disable-nls --enable-languages=c,c++,f77,ada,objc,java --disable-win32-registry --disable-shared --enable-sjlj-exceptions --enable-libgcj --disable-java-awt --without-x --enable-java-gc=boehm --disable-libgcj-debug --enable-interpreter --enable-hash-synchronization --enable-libstdcxx-debug
Thread model: win32
gcc version 3.4.5 (mingw-vista special r3)

getchar在实际EOF之前返回EOF

0 个答案: