从文本内容中提取有效信息

例如a.txt中有如下内容
$ABC,eqwe,0123,N,we23,E,234
$ABD,fkjd,2454,N,fwer,E,456
$AB,fhew,9478,N,wewf,E,rnju
$ABC,wefn,9834,N,riwqj,E,42

要求：

提取的有效信息为

eqwe,0123,we23

wefn,9834,riwqj

代码实现：

#include
#include
#include
#include
#include
int i=0; //存放信息时使用
int main(){
    int fd=open( "a.txt" ,O_RDONLY,0644);

    char c; //取出每一个字符
    ssize_t bytes;
    char xinxi[256]; //存放提取信息
    if (fd==-1)
    {
        perror ( "open" );
        return -1;
        }
    //不断的读
    while (bytes=(read(fd,&c, sizeof (c)))>0)
    {
        if (c== '$' )
            { //文件位置向后移动一位
            read(fd,&c, sizeof (c));
            if (c== 'A' )
            {
                            read(fd,&c, sizeof (c));
                if (c== 'B' )
                    {
                                read(fd,&c, sizeof (c));
                        if (c== 'C' )
                        {
                                    read(fd,&c, sizeof (c)); //指针移到逗号前
                                    read(fd,&c, sizeof (c)); //
                        if (c!= ',' ){
                            while (c!= 'N' ) //提取信息
                            {
                                {xinxi[i]=c; //将有用字符存入数组
                                ++i;
                                            read(fd,&c, sizeof (c));}

                            }
                                        read(fd,&c, sizeof (c)); //
                            if (c!= ',' )
                            continue ;}
                        }
                        else
                        {
                        while (c!= '\n' )
                                    read(fd,&c, sizeof (c));
                        continue ; //跳出while循环，并开始读取信息
                        }
                    }
            }
            }
    else if (c!= 'E' &&c!= ',' )
        {
        xinxi[i]=c;
        ++i;
        }
        else {
            while (c!= '\n' )
                    read(fd,&c, sizeof (c));
            continue ;}
        } //成功读取后的操作
    if (bytes==-1)
    {
        perror ( "read" );
        return -1;
        }
        int m;
        for (m=0;xinxi[m];++m)
            printf ( "%c" ,xinxi[m]);
            printf ( "\n" );

    return 0;
    }