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cmd/cgo: doc updates

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1. note that to use C.free <stdlib.h> must be included
2. can also extract errno from a void C function

R=golang-dev, adg
CC=golang-dev
https://golang.org/cl/6935045
This commit is contained in:
Shenghou Ma 2013-01-22 02:52:34 +08:00
parent e00c9f0dbb
commit faaa7c07d7
1 changed files with 7 additions and 4 deletions
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11
src/cmd/cgo/doc.go
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@ -65,11 +65,13 @@ struct_, union_, or enum_, as in C.struct_stat.
Go structs cannot embed fields with C types. Go structs cannot embed fields with C types.
Any C function that returns a value may be called in a multiple Any C function (even void functions) may be called in a multiple
assignment context to retrieve both the return value and the assignment context to retrieve both the return value (if any) and the
C errno variable as an error. For example: C errno variable as an error (use _ to skip the result value if the
function returns void). For example:
n, err := C.atoi("abc") n, err := C.atoi("abc")
_, err := C.voidFunc()
In C, a function argument written as a fixed size array In C, a function argument written as a fixed size array
actually requires a pointer to the first element of the array. actually requires a pointer to the first element of the array.
@ -83,7 +85,8 @@ by making copies of the data. In pseudo-Go definitions:
// Go string to C string // Go string to C string
// The C string is allocated in the C heap using malloc. // The C string is allocated in the C heap using malloc.
// It is the caller's responsibility to arrange for it to be // It is the caller's responsibility to arrange for it to be
// freed, such as by calling C.free. // freed, such as by calling C.free (be sure to include stdlib.h
// if C.free is needed).
func C.CString(string) *C.char func C.CString(string) *C.char
// C string to Go string // C string to Go string