aide pour comprendre un code

bonsoir,
je suis entrain de "décripter" un long code en c++ qui me fait tourner la tête, 'jaurais besoin de vous pour m'aider à comprendre quelque bouts:
voici en premier lieu la ligne suivante:
int Agent::uidcnt_;
dans mon fichier .h , uidcnt_ est variable protected int static ce qui explique qu'on l'appelle précédé par le nom de la classe, la question qui se pose, pourquoi appeler une variable comme sa! alors qu'il n'ya ni affectation ni rien du tout!
c'est même pas une déclaration puisque je l'ai trouvé dans mon fichier .cc
j'ai pas posté les deux .h et .cc car ils sont trés long.
merci de m'aider ^^

Très bonne question. Mais tu auras meilleur réponse si tu demandes à l'auteur des fichiers en question.

:( je le connais pas!
bref je poste quand même les codes, peut être qu'un truc m'a echappé!
*agent.h

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/* -*- Mode:C++; c-basic-offset:8; tab-width:8; indent-tabs-mode:t -*- */   #ifndef ns_agent_h #define ns_agent_h   #include "connector.h" #include "packet.h" #include "timer-handler.h" #include "ns-process.h" #include "app.h" //#include "basetrace.h" #define TIME_FORMAT "%.15g" // TIME_FORMAT is in basetrace.h, but including that header leads to problems     #define TIMER_IDLE 0 #define TIMER_PENDING 1   /*  * Note that timers are now implemented using timer-handler.{cc,h}  */   #define TRACEVAR_MAXVALUELENGTH 128   class Application;     // store old value of traced vars // work only for TracedVarTcl struct OldValue { TracedVar *var_; char val_[TRACEVAR_MAXVALUELENGTH]; struct OldValue *next_; };   class EventTrace; class Agent : public Connector { public: Agent(packet_t pktType); virtual ~Agent(); void recv(Packet*, Handler*);   //added for edrop tracing - ratul void recvOnly(Packet *) {};   void send(Packet* p, Handler* h) { target_->recv(p, h); } virtual void timeout(int tno);   virtual void sendmsg(int sz, AppData*, const char* flags = 0); virtual void send(int sz, AppData *data) { sendmsg(sz, data, 0); } virtual void sendto(int sz, AppData*, const char* flags, nsaddr_t dst); virtual void sendto(int sz, AppData*, const char* flags, ns_addr_t dst);   virtual void sendmsg(int nbytes, const char *flags = 0); virtual void send(int nbytes) { sendmsg(nbytes); } virtual void sendto(int nbytes, const char* flags, nsaddr_t dst); virtual void sendto(int nbytes, const char* flags, ns_addr_t dst); virtual void connect(nsaddr_t dst); virtual void close(); virtual void listen(); virtual void attachApp(Application* app); virtual int& size() { return size_; } inline nsaddr_t& addr() { return here_.addr_; } inline nsaddr_t& port() { return here_.port_; } inline nsaddr_t& daddr() { return dst_.addr_; } inline nsaddr_t& dport() { return dst_.port_; } void set_pkttype(packet_t pkttype) { type_ = pkttype; } inline packet_t get_pkttype() { return type_; }   protected: int command(int argc, const char*const* argv); virtual void delay_bind_init_all(); virtual int delay_bind_dispatch(const char *varName, const char *localName, TclObject *tracer);   virtual void recvBytes(int bytes); virtual void idle(); Packet* allocpkt() const; // alloc + set up new pkt Packet* allocpkt(int) const; // same, but w/data buffer void initpkt(Packet*) const; // set up fields in a pkt   ns_addr_t here_; // address of this agent ns_addr_t dst_; // destination address for pkt flow int size_; // fixed packet size packet_t type_; // type to place in packet header int fid_; // for IPv6 flow id field int prio_; // for IPv6 prio field int flags_; // for experiments (see ip.h) int defttl_; // default ttl for outgoing pkts   #ifdef notdef int seqno_; /* current seqno */ int class_; /* class to place in packet header */ #endif   static int uidcnt_;   Tcl_Channel channel_; char *traceName_; // name used in agent traces OldValue *oldValueList_;   Application *app_; // ptr to application for callback   virtual void trace(TracedVar *v); void deleteAgentTrace(); void addAgentTrace(const char *name); void monitorAgentTrace(); OldValue* lookupOldValue(TracedVar *v); void insertOldValue(TracedVar *v, const char *value); void dumpTracedVars();   /* support for event-tracing */ EventTrace *et_; virtual void trace_event(char *eventtype){}   private: void flushAVar(TracedVar *v); };   #endif

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*agent.cc

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/* -*- Mode:C++; c-basic-offset:8; tab-width:8; indent-tabs-mode:t -*- */     #ifndef lint static const char rcsid[] = "@(#) $Header: /cvsroot/nsnam/ns-2/common/agent.cc,v 1.79 2006/02/21 15:20:17 mahrenho Exp $ (LBL)"; #endif   #include <assert.h> #include <stdlib.h>   #include "config.h" #include "agent.h" #include "ip.h" #include "flags.h" #include "address.h" #include "app.h" #ifdef HAVE_STL #include "nix/hdr_nv.h" #include "nix/nixnode.h" #endif //HAVE_STL       #ifndef min #define min(a, b) (((a) < (b)) ? (a) : (b)) #endif   static class AgentClass : public TclClass { public: AgentClass() : TclClass("Agent") {} TclObject* create(int, const char*const*) { return (new Agent(PT_NTYPE)); } } class_agent;   int Agent::uidcnt_; /* running unique id */   Agent::Agent(packet_t pkttype) : size_(0), type_(pkttype), channel_(0), traceName_(NULL), oldValueList_(NULL), app_(0), et_(0) { }   void Agent::delay_bind_init_all() { delay_bind_init_one("agent_addr_"); delay_bind_init_one("agent_port_"); delay_bind_init_one("dst_addr_"); delay_bind_init_one("dst_port_"); delay_bind_init_one("fid_"); delay_bind_init_one("prio_"); delay_bind_init_one("flags_"); delay_bind_init_one("ttl_"); delay_bind_init_one("class_"); Connector::delay_bind_init_all(); }   int Agent::delay_bind_dispatch(const char *varName, const char *localName, TclObject *tracer) { if (delay_bind(varName, localName, "agent_addr_", (int*)&(here_.addr_), tracer)) return TCL_OK; if (delay_bind(varName, localName, "agent_port_", (int*)&(here_.port_), tracer)) return TCL_OK; if (delay_bind(varName, localName, "dst_addr_", (int*)&(dst_.addr_), tracer)) return TCL_OK; if (delay_bind(varName, localName, "dst_port_", (int*)&(dst_.port_), tracer)) return TCL_OK; if (delay_bind(varName, localName, "fid_", (int*)&fid_, tracer)) return TCL_OK; if (delay_bind(varName, localName, "prio_", (int*)&prio_, tracer)) return TCL_OK; if (delay_bind(varName, localName, "flags_", (int*)&flags_, tracer)) return TCL_OK; if (delay_bind(varName, localName, "ttl_", &defttl_, tracer)) return TCL_OK; if (delay_bind(varName, localName, "class_", (int*)&fid_, tracer)) return TCL_OK; return Connector::delay_bind_dispatch(varName, localName, tracer); }     Agent::~Agent() { if (oldValueList_ != NULL) { OldValue *p = oldValueList_; while (oldValueList_ != NULL) { oldValueList_ = oldValueList_->next_; delete p; p = oldValueList_; } } }   int Agent::command(int argc, const char*const* argv) { Tcl& tcl = Tcl::instance(); if (argc == 2) { if (strcmp(argv[1], "delete-agent-trace") == 0) { if ((traceName_ == 0) || (channel_ == 0)) return (TCL_OK); deleteAgentTrace(); return (TCL_OK); } else if (strcmp(argv[1], "show-monitor") == 0) { if ((traceName_ == 0) || (channel_ == 0)) return (TCL_OK); monitorAgentTrace(); return (TCL_OK); } else if (strcmp(argv[1], "close") == 0) { close(); return (TCL_OK); } else if (strcmp(argv[1], "listen") == 0) { listen(); return (TCL_OK); } else if (strcmp(argv[1], "dump-namtracedvars") == 0) { enum_tracedVars(); return (TCL_OK); }   } else if (argc == 3) { if (strcmp(argv[1], "attach") == 0) { int mode; const char* id = argv[2]; channel_ = Tcl_GetChannel(tcl.interp(), (char*)id, &mode); if (channel_ == 0) { tcl.resultf("trace: can't attach %s for writing", id); return (TCL_ERROR); } return (TCL_OK); } else if (strcmp(argv[1], "add-agent-trace") == 0) { // we need to write nam traces and set agent trace name if (channel_ == 0) { tcl.resultf("agent %s: no trace file attached", name_); return (TCL_OK); } addAgentTrace(argv[2]); return (TCL_OK); } else if (strcmp(argv[1], "connect") == 0) { connect((nsaddr_t)atoi(argv[2])); return (TCL_OK); } else if (strcmp(argv[1], "send") == 0) { sendmsg(atoi(argv[2])); return (TCL_OK); } else if (strcmp(argv[1], "set_pkttype") == 0) { set_pkttype(packet_t(atoi(argv[2]))); return (TCL_OK); } } else if (argc == 4) { if (strcmp(argv[1], "sendmsg") == 0) { sendmsg(atoi(argv[2]), argv[3]); return (TCL_OK); } } else if (argc == 5) { if (strcmp(argv[1], "sendto") == 0) { sendto(atoi(argv[2]), argv[3], (nsaddr_t)atoi(argv[4])); return (TCL_OK); } } if (strcmp(argv[1], "tracevar") == 0) { // wrapper of TclObject's trace command, because some tcl // agents (e.g. srm) uses it. const char* args[4]; char tmp[6]; strcpy(tmp, "trace"); args[0] = argv[0]; args[1] = tmp; args[2] = argv[2]; if (argc > 3) args[3] = argv[3]; return (Connector::command(argc, args)); } return (Connector::command(argc, argv)); }   void Agent::flushAVar(TracedVar *v) { char wrk[256], value[128]; int n;   // XXX we need to keep track of old values. What's the best way? v->value(value, 128); if (strcmp(value, "") == 0) // no value, because no writes has occurred to this var return; sprintf(wrk, "f -t "TIME_FORMAT" -s %d -d %d -n %s -a %s -o %s -T v -x", Scheduler::instance().clock(), addr(), dst_.addr_, v->name(), traceName_, value); n = strlen(wrk); wrk[n] = '\n'; wrk[n+1] = 0; (void)Tcl_Write(channel_, wrk, n+1); }   void Agent::deleteAgentTrace() { char wrk[256];   // XXX we don't know InstVar outside of Tcl! Is there any // tracedvars hidden in InstVar? If so, shall we have a tclclInt.h? TracedVar* var = tracedvar_; for ( ; var != 0; var = var->next_) flushAVar(var);   // we need to flush all var values to trace file, // so nam can do backtracing sprintf(wrk, "a -t "TIME_FORMAT" -s %d -d %d -n %s -x", Scheduler::instance().clock(), here_.addr_, dst_.addr_, traceName_); if (traceName_ != NULL) delete[] traceName_; traceName_ = NULL; }   OldValue* Agent::lookupOldValue(TracedVar *v) { OldValue *p = oldValueList_; while ((p != NULL) && (p->var_ != v)) p = p->next_; return p; }   void Agent::insertOldValue(TracedVar *v, const char *value) { OldValue *p = new OldValue; assert(p != NULL); strncpy(p->val_, value, min(strlen(value)+1, TRACEVAR_MAXVALUELENGTH)); p->var_ = v; p->next_ = NULL; if (oldValueList_ == NULL) oldValueList_ = p; else { p->next_ = oldValueList_; oldValueList_ = p; } }   // callback from traced variable updates void Agent::trace(TracedVar* v) { if (channel_ == 0) return; char wrk[256], value[128]; int n;   // XXX we need to keep track of old values. What's the best way? v->value(value, 128);   // XXX hack: how do I know ns has not started yet? // if there's nothing in value, return static int started = 0; if (!started) { Tcl::instance().evalc("[Simulator instance] is-started"); if (Tcl::instance().result()[0] == '0') // Simulator not started, do nothing return; // remember for next time (so we don't always have to call to tcl) started = 1; };   OldValue *ov = lookupOldValue(v); if (ov != NULL) { sprintf(wrk, "f -t "TIME_FORMAT" -s %d -d %d -n %s -a %s -v %s -o %s -T v", Scheduler::instance().clock(), here_.addr_, dst_.addr_, v->name(), traceName_, value, ov->val_); strncpy(ov->val_, value, min(strlen(value)+1, TRACEVAR_MAXVALUELENGTH)); } else { // if there is value, insert it into old value list sprintf(wrk, "f -t "TIME_FORMAT" -s %d -d %d -n %s -a %s -v %s -T v", Scheduler::instance().clock(), here_.addr_, dst_.addr_, v->name(), traceName_, value); insertOldValue(v, value); } n = strlen(wrk); wrk[n] = '\n'; wrk[n+1] = 0; (void)Tcl_Write(channel_, wrk, n+1); }   void Agent::monitorAgentTrace() { char wrk[256]; int n; double curTime = (&Scheduler::instance() == NULL ? 0 : Scheduler::instance().clock());   sprintf(wrk, "v -t "TIME_FORMAT" -e monitor_agent %d %s", curTime, here_.addr_, traceName_); n = strlen(wrk); wrk[n] = '\n'; wrk[n+1] = 0; if (channel_) (void)Tcl_Write(channel_, wrk, n+1); }   void Agent::addAgentTrace(const char *name) { char wrk[256]; int n; double curTime = (&Scheduler::instance() == NULL ? 0 : Scheduler::instance().clock());   sprintf(wrk, "a -t "TIME_FORMAT" -s %d -d %d -n %s", curTime, here_.addr_, dst_.addr_, name); n = strlen(wrk); wrk[n] = '\n'; wrk[n+1] = 0; if (channel_) (void)Tcl_Write(channel_, wrk, n+1); // keep agent trace name if (traceName_ != NULL) delete[] traceName_; traceName_ = new char[strlen(name)+1]; strcpy(traceName_, name); }   void Agent::timeout(int) { }   /*  * Callback to application to notify the reception of a number of bytes  */ void Agent::recvBytes(int nbytes) { if (app_) app_->recv(nbytes); }   /*  * Callback to application to notify the termination of a connection  */ void Agent::idle() { if (app_) app_->resume(); }   /*  * Assign application pointer for callback purposes  */ void Agent::attachApp(Application *app) { app_ = app; }   void Agent::close() { }   void Agent::listen() { }   /*  * This function is a placeholder in case applications want to dynamically  * connect to agents (presently, must be done at configuration time).  */ void Agent::connect(nsaddr_t /*dst*/) { /* dst_ = dst; */ }   /*  * Place holders for sending application data  */   void Agent::sendmsg(int /*sz*/, AppData* /*data*/, const char* /*flags*/) { fprintf(stderr, "Agent::sendmsg(int, AppData*, const char*) not implemented\n"); abort(); }   void Agent::sendmsg(int /*nbytes*/, const char* /*flags*/) { }   void Agent::sendto(int /*sz*/, AppData* /*data*/, const char* /*flags*/, nsaddr_t /*dst*/) { fprintf(stderr, "Agent::sendmsg(int, AppData*, const char*) not implemented\n"); abort(); }   // to support application using message passing void Agent::sendto(int /*sz*/, AppData* /*data*/, const char* /*flags*/, ns_addr_t /*dst*/) { }   /*  * This function is a placeholder in case applications want to dynamically  * connect to agents (presently, must be done at configuration time).  */ void Agent::sendto(int /*nbytes*/, const char /*flags*/[], nsaddr_t /*dst*/) { /* dst_ = dst; sendmsg(nbytes, flags); */ } // to support application using message passing void Agent::sendto(int /*nbytes*/, const char /*flags*/[], ns_addr_t /*dst*/) { }   void Agent::recv(Packet* p, Handler*) { if (app_) app_->recv(hdr_cmn::access(p)->size()); /* * didn't expect packet (or we're a null agent?) */ Packet::free(p); }   /*  * initpkt: fill in all the generic fields of a pkt  */   void Agent::initpkt(Packet* p) const { hdr_cmn* ch = hdr_cmn::access(p); ch->uid() = uidcnt_++; ch->ptype() = type_; ch->size() = size_; ch->timestamp() = Scheduler::instance().clock(); ch->iface() = UNKN_IFACE.value(); // from packet.h (agent is local) ch->direction() = hdr_cmn::NONE;   ch->error() = 0; /* pkt not corrupt to start with */   hdr_ip* iph = hdr_ip::access(p); iph->saddr() = here_.addr_; iph->sport() = here_.port_; iph->daddr() = dst_.addr_; iph->dport() = dst_.port_;   //DEBUG //if (dst_ != -1) // printf("pl break\n");   iph->flowid() = fid_; iph->prio() = prio_; iph->ttl() = defttl_;   hdr_flags* hf = hdr_flags::access(p); hf->ecn_capable_ = 0; hf->ecn_ = 0; hf->eln_ = 0; hf->ecn_to_echo_ = 0; hf->fs_ = 0; hf->no_ts_ = 0; hf->pri_ = 0; hf->cong_action_ = 0; hf->qs_ = 0; #ifdef HAVE_STL   hdr_nv* nv = hdr_nv::access(p); if (0) printf("Off hdr_nv %d, ip_hdr %d myaddr %d\n", hdr_nv::offset(), hdr_ip::offset(), here_.addr_); NixNode* pNixNode = NixNode::GetNodeObject(here_.addr_); // if (0) // printf("Node Object %p\n", reinterpret_cast<void *>(pNixNode) ); if (pNixNode) { // If we get non-null, indicates nixvector routing in use // Delete any left over nv in the packet // Get a nixvector to the target (may create new) NixVec* pNv = pNixNode->GetNixVector(dst_.addr_); pNv->Reset(); nv->nv() = pNv; // And set the nixvec in the packet nv->h_used = 0; // And reset used portion to 0 } #endif //HAVE_STL }   /*  * allocate a packet and fill in all the generic fields  */ Packet* Agent::allocpkt() const { Packet* p = Packet::alloc(); initpkt(p); return (p); }   /* allocate a packet and fill in all the generic fields and allocate  * a buffer of n bytes for data  */ Packet* Agent::allocpkt(int n) const { Packet* p = allocpkt();   if (n > 0) p->allocdata(n);   return(p); }

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http://cpp.developpez.com/faq/cpp/?p..._static_erreur
http://cpp.developpez.com/faq/cpp/?p...SS_init_static

merci bcp JolyLoic :)
le premier lien m'eclaircit bcp la chose, mais juste une ptite question qui me reste:

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Fred.cpp   #include "Fred.h"   int Fred::j_ = some_expression_evaluating_to_an_int;   // A côté de ça, si vous souhaitez utiliser la valeur implicite des entiers static : // int Fred::j_;

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valeur implicite, c'est a dire , on assigne a j_ rien du tout, n'est ce pas?
merci encore^^

Pour un entier statique, la valeur d'initialisation si rien n'est précisé est 0 (mais je trouve que c'est plus clair de marquer =0 explicitement). Un entier qui serait une variable locale lui n'aurait aucune valeur définie. Et pour une instance de classe définie sans précision, ce serait le constructeur par défaut de la classe qui serait utilisé.