first commit

READMe.md

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+## call fortran routine from C++ function
+
+* a FORTRAN90 subroutine is like a C++ void function, and should be declared this way in the C++ code. The qualifier extern should also be used.
+* a FORTRAN90 subroutine or function expects all its arguments to be passed by reference. This generally means simply that the C++ function must pass scalar variables by reference, not value.
+* typically, when the FORTRAN90 compiler compiles the FORTRAN90 code, the names of functions and subroutines are stored with an appended underscore. In order for these names to be found by the C++ code, it is necessary that the C++ code declare and invoke the FORTRAN90 functions and subroutines with the underscore explicitly appended to the name.
+* in many cases, a FORTRAN90 compiler is simply a "front end" to a corresponding C++ compiler, as in the case of the GNU compilers gfortran and g++, or the Intel compilers ifort and icpp. This means that, as long as the corresponding compilers are used to compile the FORTRAN90 and C++ codes, it is probably possible to use either compiler to link and load the object codes; however, the load command may need to specify explicitly certain libraries associated with one of the languages. For instance, if loading using the gcc command, it is necessary to include "-l gfortran" so that the FORTRAN90 I/O libraries, among others, are included in the build.

example2.c

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+#include <stdio.h>
+
+int main (void) {
+    printf("Two plus two is %f\n", 4);
+    return 0;
+}

example3/Makefile

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+CC=gcc
+CFLAGS=-Wall
+
+main: main.o hello_fn.o
+
+clean:
+	rm -f main main.o hello_fn.o

example3/hello.h

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+void hello(const char* name);

example3/hello_fn.c

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+#include <stdio.h>
+#include "hello.h"
+
+void hello(const char* name) {
+    printf("Hello, %s!\n", name);
+}

example3/main.c

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+#include "hello.h"
+
+int main(void) {
+    hello("world, everyone");
+    return 0;
+}

example4/main.c

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+#include <math.h>
+#include <stdio.h>
+
+int main(void) {
+    double x = 2.0;
+    double y = sqrt(x);
+    printf("the square root of %f is %f \n", x, y);
+    return 0;
+}

example5/dtest.c

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+#include <stdio.h>
+
+int main(void) {
+#ifdef TEST
+    printf("TEST mode\n");
+#endif
+    printf("Running...\n");
+    printf("value of NUM is %d\n", NUM);
+    return 0;
+}

example6/.#hello.cc

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+shudws@shudws.5723:1715510568

example6/hello.cc

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+#include <iostream>
+
+int main() {
+    std::cout << "Hello, world\n";
+    return 0;
+}

hello.F90

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+program hello
+  ! this is comment line
+
+  print *, "hello world!"
+end program hello

hello.c

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+#include <stdio.h>
+
+int main (void) {
+    printf("Hello, world!\n");
+    return 0;
+}