struct - comp.lang.c

Hi, I made a simple struct and 'm trying to assign value to its members but nothing is being actually assigned (I tested it by printing it...) code : struct header{ unsigned char msgtype; unsigned char uoid[20]; unsigned char ttl; unsigned char reserved; unsigned int datalength; }; struct header h; h.msgtype=((unsigned char)0xFA); cout<<"size "<< sizeof h<<endl; //prints "28" unsigned char buf[20]; memset(h.uoid, 0, 20); memcpy(h.uoid,(unsigned char *)GetUOID((char *)node_instance_id, "hello", buf, sizeof buf),20); //GetUOID is func h.ttl=1; //prints nothing cout<<"TTL "<<h.ttl<<endl; h.reserved=0; h.datalength=strlen(myhostname)+sizeof (myport); any idea what's wrong???

On Oct 15, 2:12=A0pm, Ian Collins <ian-n...@hotmail.com> wrote: > Neel wrote: > > > any idea what's wrong??? > > You're posing C++ to a C group? > > -- > Ian Collins C++ is just cout to make it convenient to print... Question is about Struct.

Neel wrote: > On Oct 15, 2:12 pm, Ian Collins <ian-n...@hotmail.com> wrote: >> Neel wrote: >> >>> any idea what's wrong??? >> You're posing C++ to a C group? >> *Please* stop quoting signatures. > > C++ is just cout to make it convenient to print... > Question is about Struct. It's still impossible to answer without a prototype for GetUOID. Why all those horrible casts? Post something that compiles. -- Ian Collins

On Oct 15, 2:05=A0pm, Neel <a.k.v...@gmail.com> wrote: > Hi, > I made a simple struct and 'm trying to assign value to its members > but nothing is being actually assigned (I tested it by printing it...) > > code : > > struct header{ > =A0 =A0 =A0 =A0 unsigned char msgtype; > =A0 =A0 =A0 =A0 unsigned char uoid[20]; > =A0 =A0 =A0 =A0 unsigned char ttl; > =A0 =A0 =A0 =A0 unsigned char reserved; > =A0 =A0 =A0 =A0 unsigned int datalength; > > }; > > struct header h; > h.msgtype=3D((unsigned char)0xFA); > cout<<"size "<< sizeof h<<endl; =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0//prints "= 28" > unsigned char buf[20]; > memset(h.uoid, 0, 20); > memcpy(h.uoid,(unsigned char *)GetUOID((char *)node_instance_id, > "hello", buf, sizeof buf),20); =A0//GetUOID is func > h.ttl=3D1; =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 = =A0 =A0 =A0 =A0 =A0 =A0 =A0//prints nothing > cout<<"TTL "<<h.ttl<<endl; > h.reserved=3D0; > h.datalength=3Dstrlen(myhostname)+sizeof (myport); > > any idea what's wrong??? You assigned a value of 1 to h.ttl, which is of type unsigned char. What did you expect it to print out as? If you had used printf instead of the "convenient" cout, you might have gotten a clue about what's wrong. -- Fred Kleinschmidt

Neel wrote: > On Oct 15, 2:12�pm, Ian Collins <ian-n...@hotmail.com> wrote: > > Neel wrote: > > > > > any idea what's wrong??? > > > > You're posing C++ to a C group? > > > > -- > > Ian Collins > > C++ is just cout to make it convenient to print... > Question is about Struct. structs are part of C++ as well, with differences from C structs. Ask in comp.lang.c++. Brian

Neel <a.k.vora@gmail.com> writes: > On Oct 15, 2:12 pm, Ian Collins <ian-n...@hotmail.com> wrote: >> Neel wrote: >> >> > any idea what's wrong??? >> >> You're posing C++ to a C group? >> >> -- >> Ian Collins > > C++ is just cout to make it convenient to print... > Question is about Struct. At least one explanation of your problem is related to the use of << for output. Re-write as printf calls and I'll bet the problem goes away (or at least becomes clear). -- Ben.

On Oct 15, 3:53=A0pm, Ben Bacarisse <ben.use...@bsb.me.uk> wrote: > Neel <a.k.v...@gmail.com> writes: > > On Oct 15, 2:12=A0pm, Ian Collins <ian-n...@hotmail.com> wrote: > >> Neel wrote: > > >> > any idea what's wrong??? > > >> You're posing C++ to a C group? > > >> -- > >> Ian Collins > > > C++ is just cout to make it convenient to print... > > Question is about Struct. > > At least one explanation of your problem is related to the use of << > for output. =A0Re-write as printf calls and I'll bet the problem goes > away (or at least becomes clear). > > -- > Ben. thank you

Neel wrote: > Hi, > I made a simple struct and 'm trying to assign value to its members > but nothing is being actually assigned (I tested it by printing it...) > > code : /* mha: code rewritten to be C. Try it and see what happens. */ #include <stdio.h> #include <string.h> struct header { unsigned char msgtype; unsigned char uoid[20]; unsigned char ttl; unsigned char reserved; unsigned int datalength; }; unsigned char *GetUOID(int i, char *s, unsigned char *buf, size_t nchars) { char *t = (char *) buf; snprintf(t, nchars, "%s %d", s, i); return buf; } int main(void) { struct header h; unsigned char buf[20]; int node_instance_id = 42; char myhostname[] = "myhostname"; int myport; h.msgtype = 0xFA; printf("size %zu\n", sizeof h); memset(h.uoid, 0, 20); memcpy(h.uoid, GetUOID(node_instance_id, "hello", buf, sizeof buf), 20); h.ttl = 1; printf("TTL %u\n", h.ttl); h.reserved = 0; h.datalength = strlen(myhostname) + sizeof(myport); return 0; }

On Oct 15, 4:15=A0pm, Martin Ambuhl <mamb...@earthlink.net> wrote: > Neel wrote: > > Hi, > > I made a simple struct and 'm trying to assign value to its members > > but nothing is being actually assigned (I tested it by printing it...) > > > code : > > /* mha: code rewritten to be C. =A0Try it and see what happens. */ > > #include <stdio.h> > #include <string.h> > > struct header > { > =A0 =A0 =A0unsigned char msgtype; > =A0 =A0 =A0unsigned char uoid[20]; > =A0 =A0 =A0unsigned char ttl; > =A0 =A0 =A0unsigned char reserved; > =A0 =A0 =A0unsigned int datalength; > > }; > > unsigned char *GetUOID(int i, char *s, unsigned char *buf, > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 size_t nchars) > { > =A0 =A0 =A0char *t =3D (char *) buf; > =A0 =A0 =A0snprintf(t, nchars, "%s %d", s, i); > =A0 =A0 =A0return buf; > > } > > int main(void) > { > =A0 =A0 =A0struct header h; > =A0 =A0 =A0unsigned char buf[20]; > =A0 =A0 =A0int node_instance_id =3D 42; > =A0 =A0 =A0char myhostname[] =3D "myhostname"; > =A0 =A0 =A0int myport; > =A0 =A0 =A0h.msgtype =3D 0xFA; > =A0 =A0 =A0printf("size %zu\n", sizeof h); > =A0 =A0 =A0memset(h.uoid, 0, 20); > =A0 =A0 =A0memcpy(h.uoid, GetUOID(node_instance_id, "hello", buf, sizeof = buf), > =A0 =A0 =A0 =A0 =A0 =A0 20); > =A0 =A0 =A0h.ttl =3D 1; > =A0 =A0 =A0printf("TTL %u\n", h.ttl); > =A0 =A0 =A0h.reserved =3D 0; > =A0 =A0 =A0h.datalength =3D strlen(myhostname) + sizeof(myport); > =A0 =A0 =A0return 0; > > } > > Thank You