read中的count问题

Question

#include <stdio.h> #include <stdlib.h> #include <string.h> #include <errno.h> #include <unistd.h> #include <fcntl.h> #include <sys/types.h> int main(int argc,char** argv) { char *buf=malloc(atoi(argv[2])); int fn,n,lk; //printf("sizeof(buf)=%i\n",sizeof(buf)); memset(buf,0,atoi(argv[2])); if(argc!=4){     printf("openfilenew:Usage: openfilenew filename bytes read/write(1/2)\n");     exit(1); } lk=atoi(argv[3]); if((fn=open(argv[1],O_RDWR))==-1){         printf("openfilenew:open file %sfailure because %s\n",argv[1],strerror(errno));         exit(1); } switch(lk){ case 1: { int nm=0,k,count=atoi(argv[2]); while(nm<count){        k=read(fn,buf,count-nm);        if(k==-1){            printf("error:%s",strerror(errno));exit(1);}        nm=nm+k; }; /*if(n==-1){         printf("openfilenew:read file %s failure because %s \n",argv[1],strerror(errno));         free(buf);         close(fn);         exit(1); } if(n<atoi(argv[2]))     printf("openfilenwq:alread read %i bytes,< %i\n",atoi(argv[2])); */ buf[nm]=0; printf("openfilenew:we read %i bytes[nm]==%x\n",nm,buf[nm]); close(fn); free(buf); exit(0); } case 2: { printf("please input %i data of char for writing\n",atoi(argv[2])-1); int kk=0; //gets(buf); fgets((char*)buf,(int)atoi(argv[2]),stdin); printf("the act input %i bytes from stdin\n",atoi(argv[2])-1); n=write(fn,buf,atoi(argv[2])); if(n==-1)     printf("openfilenew:write to %s failure\n",argv[1]); if(n<atoi(argv[2]))     printf("openfilenew:write bytes < the act input bytes%i\n",sizeof(buf)); close(fn); exit(0);     break; } default:         printf("openfilenew:Usage: openfilenew filename bytes read/write(1/2)\n");         exit(1); } free(buf); return 0; }

Answer 1

完全是你的代码写得有问题，细心点啊，大哥：

#include <stdio.h> #include <stdlib.h> #include <string.h> #include <errno.h> #include <unistd.h> #include <fcntl.h> #include <sys/types.h> int main(int argc,char** argv) { char *buf=malloc(atoi(argv[2])); int fn,n,lk; //printf("sizeof(buf)=%i\n",sizeof(buf)); memset(buf,0,atoi(argv[2])); if(argc!=4){     printf("openfilenew:Usage: openfilenew filename bytes read/write(1/2)\n");     exit(1); } lk=atoi(argv[3]); if((fn=open(argv[1],O_RDWR))==-1){         printf("openfilenew:open file %sfailure because %s\n",argv[1],strerror(errno));         exit(1); } switch(lk){ case 1: { int nm=0,k,count=atoi(argv[2]); while(nm<count){        k=read(fn,buf,count-nm);        if(k==-1){            printf("error:%s",strerror(errno));exit(1);}        nm=nm+k; }; /*if(n==-1){         printf("openfilenew:read file %s failure because %s \n",argv[1],strerror(errno));         free(buf);         close(fn);         exit(1); } if(n<atoi(argv[2]))     printf("openfilenwq:alread read %i bytes,< %i\n",atoi(argv[2])); */ buf[nm]=0; printf("openfilenew:we read %i bytes[nm]==%x\n",nm,buf[nm]); int read_cnt; for(read_cnt = 0; read_cnt < nm; read_cnt++)         printf("%c\n", buf[read_cnt]); close(fn); free(buf); exit(0); } case 2: { printf("please input %i data of char for writing\n",atoi(argv[2])-1); int kk=0; //gets(buf); fgets((char*)buf,(int)atoi(argv[2]),stdin); printf("the act input %i bytes from stdin\n",atoi(argv[2])-1); n=write(fn,buf,atoi(argv[2])); if(n==-1)     printf("openfilenew:write to %s failure\n",argv[1]); if(n<atoi(argv[2]))     printf("openfilenew:write bytes < the act input bytes%i\n",sizeof(buf)); close(fn); int cnt = 0; for (;cnt < atoi(argv[2]); cnt++)         printf("%c\n", buf[cnt]); exit(0);     break; } default:         printf("openfilenew:Usage: openfilenew filename bytes read/write(1/2)\n");         exit(1); } free(buf); return 0; }

Answer 2

我不是说读和写的问题，而是说当读时，设备驱动程序的file相应read函数里边count反应出来的问题：
ssize_t do_short_read (struct inode *inode, struct file *filp, char __user *buf, size_t count, loff_t *f_pos)
{
printk(KERN_ALERT "short: count of do_short_read function = %i\n",count);
....
}

针对测试程序：
case 1:
{
int nm=0,k,count=atoi(argv[2]);
while(nm<count){
       k=read(fn,buf,count-nm);
       if(k==-1){
           printf("error:%s",strerror(errno));exit(1);}
       nm=nm+k;
};
这里面的read的count和驱动程序里面do_short_read的count不一致.

[ 本帖最后由 whoisliang 于 2009-1-20 17:08 编辑 ]

Answer 3

#include <stdio.h> #include <stdlib.h> #include <string.h> #include <errno.h> #include <unistd.h> #include <fcntl.h> #include <sys/types.h> int main(int argc,char** argv) { char *buf=malloc(atoi(argv[2])); int fn,n,lk; //printf("sizeof(buf)=%i\n",sizeof(buf)); memset(buf,0,atoi(argv[2])); if(argc!=4){     printf("openfilenew:Usage: openfilenew filename bytes read/write(1/2)\n");     exit(1); } lk=atoi(argv[3]); if((fn=open(argv[1],O_RDWR))==-1){         printf("openfilenewpen file %sfailure because %s\n",argv[1],strerror(errno));         exit(1); } switch(lk){ case 1: { int nm=0,k,count=atoi(argv[2]); while(nm<count){        k=read(fn,buf,count-nm);        if(k==-1){            printf("error:%s",strerror(errno));exit(1);}        nm=nm+k; }; /*if(n==-1){         printf("openfilenew:read file %s failure because %s \n",argv[1],strerror(errno));         free(buf);         close(fn);         exit(1); } if(n<atoi(argv[2]))     printf("openfilenwq:alread read %i bytes,< %i\n",atoi(argv[2])); */ buf[nm]=0; printf("openfilenew:we read %i bytes[nm]==%x\n",nm,buf[nm]); close(fn); free(buf); exit(0); } case 2: { printf("please input %i data of char for writing\n",atoi(argv[2])-1); int kk=0; //gets(buf); fgets((char*)buf,(int)atoi(argv[2]),stdin); printf("the act input %i bytes from stdin\n",atoi(argv[2])-1); n=write(fn,buf,atoi(argv[2])); if(n==-1)     printf("openfilenew:write to %s failure\n",argv[1]); if(n<atoi(argv[2]))     printf("openfilenew:write bytes < the act input bytes%i\n",sizeof(buf)); close(fn); int cnt = 0; for (;cnt < atoi(argv[2]); cnt++)         printf("%d\n", buf[cnt]); exit(0);     break; } default:         printf("openfilenew:Usage: openfilenew filename bytes read/write(1/2)\n");         exit(1); } free(buf); return 0; }

Answer 4

刚才写一个进程调度的体会去了,现在看到你的回复,先谢了!

我明白你的意思了.就算我输入时不带空格输入123456789,读6个字符的时候,驱动程序read函数中 count应该等于6才对吧,我没有用C库调用,直接采用系统调用的方式,这是你以前说的,应该不会错.可是结果依然不理解?????????

Answer 5

无人回答吗？
不会这么个简单问题都回答不出来吧？
各位。。。。。。。。。。。。。。。？？？？？？？？？？？？