英文:
Why is this string blank after the procedure returns it (Odin)?
问题
在以下的小示例程序中，从 stdin 读取输入。在 read_input 函数中，打印字符串值有效，但在 main 函数中不起作用。令人惊讶的是，在 main 函数中可以输出字符串的长度 (len)，但字符串本身却是空的。
main :: proc() {
fmt.print("$ ")
input := read_input()
// This will output the proper length
fmt.println("returned string length:", len(input))
// This will be empty
fmt.println("returned string: ", input)
}
read_input :: proc() -> string {
buf: [256]byte
num_bytes, err := os.read(os.stdin, buf[:])
if err < 0 {
return "Error reading from stdin"
}
str := string(buf[:num_bytes - 1])
// this will output the proper number of bytes
fmt.println("bytes read: ", num_bytes)
// this will output the string entered, minus the newline
fmt.println("read string: ", str)
return str
}
示例运行/输出:
$ hello
bytes read: 6
read string: hello
returned string length: 5
returned string:
我发现返回 strings.clone(str) 可行，但我并没有真正理解上面的问题。
英文:
In the following small sample program, input is read from stdin. Printing the string value works inside read_input, but not in main. Surprisingly, the length (len) of the string does output in main, though the string output is blank.
main :: proc() {
fmt.print("$ ")
input := read_input()
// This will output the proper length
fmt.println("returned string length:", len(input))
// This will be empty
fmt.println("returned string: ", input)
}
read_input :: proc() -> string {
buf: [256]byte
num_bytes, err := os.read(os.stdin, buf[:])
if err < 0 {
return "Error reading from stdin"
}
str := string(buf[:num_bytes - 1])
// this will output the proper number of bytes
fmt.println("bytes read: ", num_bytes)
// this will output the string entered, minus the newline
fmt.println("read string: ", str)
return str
}
Example run/output:
$ hello
bytes read: 6
read string: hello
returned string length: 5
returned string:
I've discovered that returning strings.clone(str) works but I'm not really understanding the problem above.
答案1
得分: 1
在Odin中，string只是对底层数据缓冲区的一个视图。在您的情况下，它指向buf，而buf是局部于read_input过程的。一旦read_input返回，它的堆栈内存就消失了，但返回的字符串仍然指向它。
strings.clone(str)之所以起作用，是因为它为字符串复制分配了内存，并返回指向这个内存的字符串。在这种情况下，您需要在main函数中进行delete操作，以避免内存泄漏。
英文:
In Odin string is just a view over underlaying data buffer. In your case it points to buf which is local to read_input procedure. Once read_input returns its stack memory is gone, but returned string still points to it.
strings.clone(str) works because it allocates memory for a string copy and return string which points into this memory. In this case you'll need to delete it in main to avoid memory leak.
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