Program Entry Point

The entry point of a Cangjie program is main. At the top level of the package in the root directory of the source files, there can be at most one main function.

When compiling a module into an executable, the compiler only searches for main at the top level of the root directory’s source files. If no main is found, the compiler will report an error. If main is found, the compiler will further verify its parameter and return types. Note that main cannot be modified by access modifiers. When a package is imported, any main defined within that package will not be imported.

The main function serving as the program entry point can either have no parameters or accept a parameter of type Array<String>. Its return type must be either Unit or an integer type.

Example of main without parameters:

// main.cj
main(): Int64 { // OK.
    return 0
}

Example of main with Array<String> parameter:

// main.cj
main(args: Array<String>): Unit { // OK.
    for (arg in args) {
        println(arg)
    }
}

After compiling with cjc main.cj, executing via command line: ./main Hello, World will produce the following output:

Hello,
World

Below are some incorrect examples:

// main.cj
main(): String { // Error, return type of 'main' is not 'Integer' or 'Unit'.
    return ""
}

// main.cj
main(args: Array<Int8>): Int64 { // Error, 'main' cannot be defined with parameter whose type is not Array<String>.
    return 0
}

// main.cj
// Error, multiple 'main's are found in source files.
main(args: Array<String>): Int32 {
    return 0
}

main(): Int8 {
    return 0
}