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r-print-value-from-c
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| #include <R_ext/Parse.h> | |
| const char* r_print_value(SEXP x) { | |
| // Assign `x` into the global environment under the name `.debug` | |
| Rf_defineVar(Rf_install(".debug"), x, R_GlobalEnv); | |
| // This is the R code that we want to run to print `.debug` and then capture all its printed output | |
| const char* command = "paste0(capture.output(print(.debug)), collapse = '\n')"; | |
| SEXP command_sexp = PROTECT(Rf_allocVector(STRSXP, 1)); | |
| SET_STRING_ELT(command_sexp, 0, Rf_mkCharCE(command, CE_UTF8)); | |
| // Parse that command into an actual R expression we can evaluate | |
| // (This is a little fiddly because `R_ParseVector()` returns a vector of expressions, | |
| // but we know we only expect to get exactly 1 expression back) | |
| ParseStatus status; | |
| SEXP expressions = PROTECT(R_ParseVector(command_sexp, -1, &status, R_NilValue)); | |
| if (status != PARSE_OK) { | |
| Rf_error("failed"); | |
| } | |
| if (Rf_xlength(expressions) != 1) { | |
| Rf_error("expected a single expression"); | |
| } | |
| SEXP command_expr = VECTOR_ELT(expressions, 0); | |
| // Ok, now evaluate the R code `command` from above in the global env, where `.debug` exists | |
| SEXP output = Rf_eval(command_expr, R_GlobalEnv); | |
| R_PreserveObject(output); | |
| // We expect the result to be a character vector of length 1 containing the captured output | |
| SEXP elt = STRING_ELT(output, 0); | |
| const char* v_elt = CHAR(elt); | |
| UNPROTECT(2); | |
| return v_elt; | |
| } |
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Thanks so much for this, Davis! @hturner and I used this today and it was super great.
Just to build on this, here is what we did in order to get this to work with Devel R.
We created a C file, named
zzz.cinsrc/main/zzz.c, and also had to have the following header files in the below order. Then we also had to add a line to the (already existing) makefile,Makefile.ininsrc/main/Makefile.in, where we added a linezzz.cunderSOURCES_C = \.Then we did the regular debug stuff:
Sys.getpid()call r_execute_and_capture(a)to see output.Thanks again for your help with this!