CODEWITHSUNDEEP
javac++candroid-ndkjava-native-interface
smileVann
smileVann

Reputation: 554

how data types in the Java programming language map to the data types in native programming languages such as C and C++,specifically

chapter 3 of the book "the Java Native Interface Programmer’s Guide and Specification",which says "The mapping of primitive types is straightforward",I'm a little confused about the sentence. As we know that the size of c data types is uncertain,it depends on the environment where the program run ,complie... such as the size of int type may be 2 bytes or 4 bytes. But the size of java data types is definite.the size of int is 4 bytes.

so,how does jni map the data types between java and c/c++ clearly.

any answers will be appreciated!

Upvotes: 2

Views: 490

Answers (2)

fadden
fadden

Reputation: 52343

The jni.h header defines appropriate primitive types: jint, jlong, jchar, and so on. These are declared to match the sizes of the corresponding Java primitives. Use these in your JNI code.

Upvotes: 1

Ray Toal
Ray Toal

Reputation: 88418

Well, in C, there is a module called stdint.h which defines the types int64_t, int32_t, and friends, which does make the mapping "straightforward."

But you're right to note that in any particular implementation of C, the size of plain old int is not specified exactly. The author was indeed pretty loose with the word "straightforward," and was assuming you would read the claim as something like "Java's int maps to the C signed integer type of 32 bits."

Upvotes: 1

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