<fopen 관련> "w" 모드로 연 파일엔 써지는데.. "w+" 모드로 연 파일엔 안 써짐

#include "engine_header.h"

//PORT : port number through which we can access target site
#define PORT 80

//MAXBUFSIZE : maximum capacity of buffer for retrieving web page from remote site
#define MAXBUFSIZE 20000

int ret_html(char *target_site,char *msg_to_server,pid_t crawler_pid,int doc_num)
{
int sockfd,numbytes;
char buf[MAXBUFSIZE+1]; //buffer for retrieving web text
struct hostent *he;
struct sockaddr_in their_addr;

char *prefix="txt_from_html"; //prefix to be attached to the output filename
char tmpfile[50]; //Temporary file storing raw html document
char txtfile[50];
//Text file which resulted from temporary html document by eliminating tags

//-------------------------------------------------------------------------------
//Create filename : tmp__.txt for raw html file
// __.txt for tag_eliminated file
//To show which crawler has retrieved that page, attach crawler_pid to filename
//To show document number , attach doc_num to file name
//To show this file is text file, attach expension '.txt' to the file name
//-------------------------------------------------------------------------------

sprintf(tmpfile,"%s%d%s%d%s","html_",(int)crawler_pid,"_",doc_num,".txt");
//is a temporary file name storing raw html document
sprintf(txtfile,"%s%s%d%s%d%s",prefix,"_",(int)crawler_pid,"_",doc_num,".txt");
//is a tag-eliminated text file name

//------------------------------------------------------------------------------
FILE *raw_html_fd; //FILE structure for raw html document
FILE *tag_eliminated_fd; //FILE structure for tag-eliminated html document

if((raw_html_fd=fopen(tmpfile,"w"))==NULL)
{
fatal("Could not open temporary file for storing raw html document");
}

if((tag_eliminated_fd=fopen(txtfile,"w"))==NULL)
{
fatal("Could not open tag-eliminated file");
}
//------------------------------------------------------------------------------

if((he=gethostbyname(target_site))==NULL) {
herror("gethostbyname in ret_html()");
printf("%d\n",h_errno);
exit(1);
}

if((sockfd=socket(AF_INET,SOCK_STREAM,0))==-1)
{
fatal("socket in ret_html()");
}

their_addr.sin_family=AF_INET;
their_addr.sin_port=htons(PORT);
their_addr.sin_addr=*((struct in_addr *)he->h_addr);
bzero(&(their_addr.sin_zero),8);

if(connect(sockfd,(struct sockaddr *)&their_addr,sizeof(struct sockaddr))==-1)
{
fatal("connect in ret_html()");
}

int bytes_sent;

if((bytes_sent=send(sockfd,msg_to_server,strlen(msg_to_server),0))==-1)
{
fatal("send in ret_html()");
}

//----------------------------------------------------------------
//Following while loop retrieve numbytes bytes from target site
//Each time search engine retrieves web page from target site,
//----------------------------------------------------------------

int i; //for couting the number of zero bytes receptions

int totalbytes=0; //for total bytes read

while((numbytes=recv(sockfd,buf,MAXBUFSIZE,0)) != -1)
{

//Test ----------------------------------------
//printf("numbytes read : %d\n",numbytes);
//Test ----------------------------------------

if(numbytes == 0)
{
i++;

if(i == 5)
{
printf("\nZero bytes received over the predefined limit\n");
break;
}
else
{
// printf("Zero bytes received\n");
sleep(1);
continue;
}
}
else
{

totalbytes += numbytes;

if(fwrite((void *)buf,sizeof(char),numbytes,raw_html_fd) != numbytes)
{
fatal("fputs in ret_html()");
}

//insert '\n' to output file to avoid 'line too long' error
putc('\n',raw_html_fd);

//Wait for receiving new message from remote web server
//(Essential part for retrieving full html document)
sleep(1);

}
}

//Test ------------------------------
printf("totalbytes : %d\n",totalbytes);
printf("numbytes : %d\n",numbytes);
//Test ------------------------------

//----------------------------------------
//Eliminate tags from raw html document
//----------------------------------------
tag_eliminator(raw_html_fd,tag_eliminated_fd);

//Test --------------
printf("raw HTML file : %s\n",tmpfile);
//------------------

//----------------------
//Close file descriptor
//----------------------
fclose(raw_html_fd);
fclose(tag_eliminated_fd);

//---------------------------
//Close socket descriptor
//----------------------------
close(sockfd);

return 0;
}

감사합니다..^^

doldori 님께서 말씀하신대로 하니까 정상적으로 동작하네요..^^

예상하신 것과 같이 tag_eliminator() 내부에 getc(raw_html_fd) 를 호출하는 부분이 있었습니다.

tag_eliminator() 를 호출하는 부분을 주석처리한 경우와,
tag_eliminator() 를 호출하되, 말씀하신 것처럼 rewind(raw_html_fd) 를 먼저 호출한 경우에 대해서 실행시켜 봤는데.. 정상적으로 동작합니다.

그런데.. 일단 파일에 쓰는 작업을 마친 후에, 별도의 함수(tag_eliminator) 를 호출해 읽는 작업을 수행하는데.. 파일에 써지는 건 제대로 써져야 하는 거 아닌가요?

w+ 로 열었으니까.. 일단 쓰는 건 제대로 써지고.. 그 후에 읽는 과정에서 rewind() 를 안 해줘서 문제가 발생한 걸로 보이는데..

문제가 읽어오는 데서 발생해야 할 것 같은데.. 왜 쓰는 것까지 영향을 받는건지 모르겠습니다...