Error linking libpq for postgreSQL conncetion

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PostgreSQL

can anybody help me out from this error?

1>------ Build started: Project: test_connection, Configuration: Debug Win32 ------
1>Compiling...
1>test_connection.cpp
1>Linking...
1>test_connection.obj : error LNK2031: unable to generate p/invoke for "extern "C" enum ConnStatusType __clrcall PQstatus(struct pg_conn const *)" (?PQstatus@@$$J0YM?AW4ConnStatusType@@PBUpg_conn@@@Z); calling convention missing in metadata
1>test_connection.obj : error LNK2031: unable to generate p/invoke for "extern "C" struct pg_conn * __clrcall PQsetdbLogin(char const *,char const *,char const *,char const *,char const *,char const *,char const *)" (?PQsetdbLogin@@$$J0YMPAUpg_conn@@PBD000000@Z); calling convention missing in metadata
1>test_connection.obj : error LNK2031: unable to generate p/invoke for "extern "C" void __clrcall PQfinish(struct pg_conn *)" (?PQfinish@@$$J0YMXPAUpg_conn@@@Z); calling convention missing in metadata
1>test_connection.obj : warning LNK4248: unresolved typeref token (01000015) for 'pg_conn'; image may not run
1>test_connection.obj : error LNK2028: unresolved token (0A000016) "extern "C" enum ConnStatusType __clrcall PQstatus(struct pg_conn const *)" (?PQstatus@@$$J0YM?AW4ConnStatusType@@PBUpg_conn@@@Z) referenced in function "private: void __clrcall test_connection::Form1::button1_Click(class System::Object ^,class System::EventArgs ^)" (?button1_Click@Form1@test_connection@@$$FA$AAMXP$AAVObject@System@@P$AAVEventArgs@4@@Z)
1>test_connection.obj : error LNK2028: unresolved token (0A000017) "extern "C" struct pg_conn * __clrcall PQsetdbLogin(char const *,char const *,char const *,char const *,char const *,char const *,char const *)" (?PQsetdbLogin@@$$J0YMPAUpg_conn@@PBD000000@Z) referenced in function "private: void __clrcall test_connection::Form1::button1_Click(class System::Object ^,class System::EventArgs ^)" (?button1_Click@Form1@test_connection@@$$FA$AAMXP$AAVObject@System@@P$AAVEventArgs@4@@Z)
1>test_connection.obj : error LNK2028: unresolved token (0A00001D) "extern "C" void __clrcall PQfinish(struct pg_conn *)" (?PQfinish@@$$J0YMXPAUpg_conn@@@Z) referenced in function "private: void __clrcall test_connection::Form1::CloseConn(struct pg_conn *)" (?CloseConn@Form1@test_connection@@$$FA$AAMXPAUpg_conn@@@Z)
1>test_connection.obj : error LNK2019: unresolved external symbol "extern "C" void __clrcall PQfinish(struct pg_conn *)" (?PQfinish@@$$J0YMXPAUpg_conn@@@Z) referenced in function "private: void __clrcall test_connection::Form1::CloseConn(struct pg_conn *)" (?CloseConn@Form1@test_connection@@$$FA$AAMXPAUpg_conn@@@Z)
1>test_connection.obj : error LNK2019: unresolved external symbol "extern "C" enum ConnStatusType __clrcall PQstatus(struct pg_conn const *)" (?PQstatus@@$$J0YM?AW4ConnStatusType@@PBUpg_conn@@@Z) referenced in function "private: void __clrcall test_connection::Form1::button1_Click(class System::Object ^,class System::EventArgs ^)" (?button1_Click@Form1@test_connection@@$$FA$AAMXP$AAVObject@System@@P$AAVEventArgs@4@@Z)
1>test_connection.obj : error LNK2019: unresolved external symbol "extern "C" struct pg_conn * __clrcall PQsetdbLogin(char const *,char const *,char const *,char const *,char const *,char const *,char const *)" (?PQsetdbLogin@@$$J0YMPAUpg_conn@@PBD000000@Z) referenced in function "private: void __clrcall test_connection::Form1::button1_Click(class System::Object ^,class System::EventArgs ^)" (?button1_Click@Form1@test_connection@@$$FA$AAMXP$AAVObject@System@@P$AAVEventArgs@4@@Z)
1>F:\Data Bayu\Project\test_connection\Debug\test_connection.exe : fatal error LNK1120: 6 unresolved externals

I got that message from debug, I'm new for this one. Can anybody help me and explain what is that mean?

Thank's for any help