Reference

The R object C representation of the R object
SEXP	Pointer to SEXPREC
SEXPREC	R's fundamental data type at C level
SEXPTYPE	Data type for coding of R data subtypes
SEXPREC_HEADER	SEXPREC_HEADER
sxpinfo_struct	struct sxpinfo_struct
Types of R objects Macros defining the internal types (SEXPTYPE) of R objects
NILSXP	The type of R's NULL
SYMSXP	The type of name and symbol objects
LISTSXP	The type of pairlist objects
CLOSXP	The type of function objects
ENVSXP	The type of environment objects
PROMSXP	The type of promise objects
LANGSXP	The type of language constructs
SPECIALSXP	The type of special forms
BUILTINSXP	The type of builtin non-special forms
CHARSXP	The type of scalar strings (internal only)
LGLSXP	The type of logical vectors
INTSXP	The type of integer vectors
REALSXP	The type of double vectors
CPLXSXP	The type of complex vectors
STRSXP	The type of character vectors
DOTSXP	The type of ... object
ANYSXP	The type of the "any" object
VECSXP	The type of generic vectors (lists)
EXPRSXP	The type of expression objects
BCODESXP	The type of byte code objects
EXTPTRSXP	The type of external pointers
WEAKREFSXP	The type of weak references
RAWSXP	The type of raw vectors
S4SXP	The type of S4, non-vector objects
NEWSXP	The type of fresh node created in new page
FREESXP	The type of R's node released by GC
FUNSXP	The pseudo-type lumping closure, builtin and special
Basic types C basic types
Rboolean	R's boolean type
Rcomplex	Rcomplex
Rbyte	Rbyte
Macros
TYPEOF	The type of an R object
NA_LOGICAL	NA_LOGICAL
Variables
R_NilValue	R_NilValue
R_LogicalNAValue	R_LogicalNAValue
R_FalseValue	R_FalseValue
R_TrueValue	R_TrueValue
Scalar conversions from C to R
Rf_ScalarLogical	Rf_ScalarLogical
Rf_ScalarInteger	Rf_ScalarInteger
Rf_ScalarReal	Rf_ScalarReal
Rf_ScalarComplex	Rf_ScalarComplex
Rf_ScalarRaw	Rf_ScalarRaw
Rf_mkCharLenCE	Rf_mkCharLenCE
Scalar conversions from R to C
Rf_asLogical	Convert an R scalar logical vector to a C int
Rf_asInteger	Convert an R scalar integer vector to a C int
Rf_asReal	Convert an R scalar double vector to a C double
CHARACTER_VALUE	Convert a scalar R object to a C string
Coercion
Rf_asChar	Coerce an R object to a scalar string (CHARSXP)
Character and Strings
Rf_asChar	Coerce an R object to a scalar string (CHARSXP)
R_CHAR	Convert a string scalar (CHARSXP) to a C-string (char *)
CHARACTER_VALUE	Convert a scalar R object to a C string
Files
Rinternals.h	Rinternals.h