This is specifically given as an example in the C++ standard when it’s discussing the intricacies of declaring external or internal linkage. It’s in section 7.1.1.7, which has this exert: static int b ; // b has internal linkage extern int b ; // b still has internal linkage extern int d ; // d … Read more
Templates aren’t actual code, they’re just guidelines to the compiler for how to generate the code once the template parameters are known. As such they don’t actually exist until you try to use them. You can’t provide linkage to something that doesn’t exist.
Yes, you are just lucky 🙂 The extern “C” is one language linkage for the C language that every C++ compiler has to support, beside extern “C++” which is the default. Compilers may supports other language linkages. GCC for example supports extern “Java” which allows interfacing with java code (though that’s quite cumbersome). extern “C” … Read more
The Bioconductor package RBGL (an R interface to the BOOST graph library) contains a function, connectedComp(), which identifies the connected components in a graph — just what you are wanting. (To use the function, you will first need to install the graph and RBGL packages, available here and here.) library(RBGL) test <- data.frame(id1=c(10,10,1,1,24,8),id2=c(1,36,24,45,300,11)) ## Convert … Read more
C and C++ are superficially similar, but each compiles into a very different set of code. When you include a header file with a C++ compiler, the compiler is expecting C++ code. If, however, it is a C header, then the compiler expects the data contained in the header file to be compiled to a … Read more
extern “C” makes a function-name in C++ have C linkage (compiler does not mangle the name) so that client C code can link to (use) your function using a C compatible header file that contains just the declaration of your function. Your function definition is contained in a binary format (that was compiled by your … Read more