[R] Accessing C source files

[ravi]

Hi all,On looking at the source code for the integrate function, I find that it has the following call:
wk <- .External(C_call_dqagi, ff, rho = environment(),             as.double(bound), inf, as.double(abs.tol), as.double(rel.tol),             limit = limit)How do I access the source code for C_call_dqagi? From other references ("Writing R-extensions section 6.9), I find a reference to Rdqagi when discussing the integrate function. I would like to know if C_call_dqagi and Rdqagi are the same.How do I access the source code for either of these functions? From the article titled "R help desk Acessing the sources" by Uwe Ligges in Rnews_2006-4, I gather that the C files can be found in the folder $R_HOME/src/main/. But when I look at the equivalent folder in R 3.6.1, I find that the main sub-folder is missing in src (the only sub-folder found there is library). I do not find any C file in the src subfolder 
Where do I find the C source files? How do I get to look at them? I have a lot of follow-up questions on interfacing with the C files, but I would like to first know where I can find them. At least on how I can access them.Thanks,Ravi Sutradhara


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