c - C 中的文件读取。 fread 函数的并发症

Question

我正在读取一个输入文件，但在读取其中的每一行时遇到了麻烦。我的输入文件有两种类型的记录。一个有 52 个字符，而另一个有 926 个字符。我不知道如何处理我的 fread 函数，以便它可以处理这两个记录。谁能帮我吗？谢谢

#define LINESZ 927     /* one extra byte for new line */
int num;               /* integer for line number */
char buffer[LINESZ];   /* buffer for file read line */

int main()
{
    FILE *ifp, *ofp;

    ifp = fopen("dd:INPUTF", "r");
    ofp = fopen("dd:OUTPUTF", "w");

    while (!feof(ifp)) {
        if (num = (fread(buffer, sizeof(char), LINESZ, ifp))) {
            if (buffer[22] == 'O') {
                printf("ravroot, %c\n", buffer[22]);
                printf("%s*\n", buffer);
            }
            else if (buffer[22] == 'A') {
                printf("ravrate, %c\n", buffer[22]);
                printf("%s*\n", buffer);
            }
        }
    }

    fclose(ifp);
    fclose(ofp);
    return(0);
}

Answer 1

从文件中读取行时，您应该使用fgets 函数。但是请注意，fgets 会将换行符写入您的缓冲区，因此您需要删除换行符。生成的代码如下所示

#define LINESZ 1024    /* lots of extra bytes, memory is cheap */
char buffer[LINESZ];   /* buffer for file read line */

int main( void )
{
    int length;
    FILE *ifp, *ofp;

    ifp = fopen("dd:INPUTF", "r");
    ofp = fopen("dd:OUTPUTF","w");

    while( fgets( buffer, LINESZ, ifp ) != NULL )
    {
        // remove the newline character, if any
        length = strlen( buffer );
        if ( length > 0 && buffer[length-1] == '\n' )
            buffer[--length] = '\0';                    

        if ( length > 22 )
        {
            if(buffer[22] == 'O')
            {
                printf("ravroot, %c\n", buffer[22]);
                printf("%s*\n", buffer);
            }
            else if(buffer[22] == 'A')
            {
                printf("ravrate, %c\n", buffer[22]);
                printf("%s*\n", buffer);
            }
        }
    }
    fclose(ifp);
    fclose(ofp);
    return(0);    
}