fgets() seems to overflow input to other variables

I'm doing a read from a file, but the input seems to "overflow" into other variables.

I have these 2 variables:

char str[250];  //used to store input from stream
char *getmsg;   //already points to some other string

The problem is, when I use fgets() to read the input

printf("1TOKEN:%s\n",getmsg);
    fp=fopen("m.txt","r");
    fp1=fopen("m1.txt","w");
        if(fp!=NULL && fp1!=NULL)
printf("2TOKEN:%s\n",getmsg);
        while(fgets(str,250,fp)!=NULL){
printf("3TOKEN:%s\n",getmsg);
        printf("read:%s",str);
printf("4TOKEN:%s\n",getmsg);

I get something like this:

1TOKEN:c
2TOKEN:c
3TOKEN:b atob atobbody

read:a b atob atobbody
4TOKEN:b atob atobbody

You see how str kind of flows into getmsg. What happened there? How can I avoid this from happening?

Thanks in advance :)

in the code, "getmsg" is called "token", I thought it might have something to do with identical names or something so I changed it to getmsg, same error, so I changed it back...

                        if(buf[0]=='C'){
                            int login_error=1;

                            fp=fopen("r.txt","r");
                            if(fp!=NULL){
                                memcpy(&count,&buf[1],2);
                                pack.boxid=ntohs(count);

                                memcpy(pack.pword,&buf[3],10);
                                printf("boxid:%u pword:%s\n",pack.boxid,pack.pword);

                                while(fgets(str,250,fp)!=NULL){

/*"getmsg"===>*/                    token=strtok(str," ");
                                    token=strtok(NULL," ");//receiver uname
                                    token1=strtok(NULL," ");//pword
                                    token2=strtok(NULL," ");//boxid
                                    sscanf(token2,"%hu",&count);//convert char[] to unsigned short

                                    if(pack.boxid==count && strcmp(token1,pack.pword)==0){//uname & pword found
                                        login_error=0;
                                        printf("found:token:%s\n",token);
                                        break;
                                    }
                                }
                                if(login_error==1){
                                    count=65535;
                                    pack.boxid=htons(count);
                                }
                                if(login_error==0){
                                    count=0;
                                    pack.boxid=htons(count);
                                }
                                fclose(fp);
                            }
printf("1TOKEN:%s\n",token);
                            if(login_error==0){
                                int msg_error=1;

                                fp=fopen("m.txt","r");
                                fp1=fopen("m1.txt","w");
                                if(fp!=NULL && fp1!=NULL){
printf("2TOKEN:%s\n",token);
                                    while(fgets(str,250,fp)!=NULL){


printf("3TOKEN:%s\n",token);
                                              printf("read:%s",str);
                                        token1=strtok(str," ");//sender
                                        token2=strtok(NULL," ");//receiver
                                        token3=strtok(NULL," ");//subject
                                        token4=strtok(NULL," ");//body
                                        printf("m.txt:token1:%s token2:%s token3:%s token4:%s\n",token1,token2,token3,token4);

                                        if(msg_error==1 && strcmp(token,token2)==0){//message found
                                            msg_error=0;
                                            count=0;
                                            pack.boxid=htons(count);
                                            strcpy(pack.uname,token1);
                                            strcpy(pack.subject,token3);
                                            strcpy(pack.body,token4);
                                            printf("pack:uname:%s subject:%s body:%s token:%s token2:%s strcmp:%d\n",pack.uname,pack.subject,pack.body,token,token2,strcmp(token,token2));
                                            continue;
                                        }

                                        fprintf(fp1,"%s %s %s %s\n",token1,token2,token3,token4);
                                    }
                                    if(msg_error==1){
                                        count=65534;
                                        pack.boxid=htons(count);
                                    }
                                    printf("count:%u -> boxid:%u\n",count,pack.boxid);

                                    fclose(fp);
                                    fclose(fp1);
                                }

                                str[0]='c';
                                memcpy(&str[1],&pack.boxid,2);
                                memcpy(&str[3],pack.uname,8);
                                memcpy(&str[11],pack.subject,20);
                                memcpy(&str[31],pack.body,200);
                                str[231]='\0';

                                bytes=232;
                            }
                        }

below is m.txt, it is used to store senders, receivers, subjects and msgbodies: the naming patter is quite obvious >.^

a b atob atobbody
a c atoc atoccc
b c btoc btoc开发者_JAVA技巧cccc
b a btoa btoaaaaa

So I'm trying to get a msg stored in m.txt for the recipient "c", but it flows over, and by much coincidence, it returns the msg for "b"...

It looks like getmsg is pointing to the third character of your str buffer:

`str` is "a b atob atobbody"
            ^
            |
            \__ `getmsg` is pointing there.

Therefore, every time you change str by calling fgets(), the string pointed to by getmsg also changes, since it uses the same memory.