英文:
Weird Compiler Errors in Go
问题
当我运行以下代码（它应该将字符串的内容反转），编译器会报错。
package mainimport "fmt"func main(){argString := "I am a string"arrayPointer := len(argString)outputString := "string"for arrayPointer >= 0 ; arrayPointer-- {outputString := fmt.Sprintf("%s%s", outputString, argString[arrayPointer])}}
它会抛出以下错误：
prog.go:9: syntax error: missing { after for clauseprog.go:12: syntax error: unexpected }[process exited with non-zero status]
我以前使用过这种语法（除非我漏掉了什么），从来没有看到过这种错误。我漏掉了什么？
英文:
When I run the following code (it's supposed to reverse the contents of a string), I get strange errors from the compiler.
package mainimport "fmt"func main(){argString := "I am a string"arrayPointer := len(argString)outputString := "string"for arrayPointer >= 0 ; arrayPointer-- {outputString := fmt.Sprintf("%s%s", outputString, argString[arrayPointer])}}
It throws the following errors:
prog.go:9: syntax error: missing { after for clauseprog.go:12: syntax error: unexpected }[process exited with non-zero status]
I've used this syntax before (unless I'm missing something), and I've never seen errors from it. What am I missing?
答案1
得分: 6
从规范来看，for语句有三种形式：
- 单个条件表达式
- 三个语句版本，包括初始化语句、条件和后置语句
- 范围子句
你的语句不符合这些形式。很可能编译器认为你使用的是第一种形式，并在arrayPointer >= 0后面没有{时报错。你可以通过改为第二种形式来修复这个问题：
for ; arrayPointer >= 0 ; arrayPointer-- {
（或者将arrayPointer的初始化语句作为for语句的第一部分）。
英文:
From the spec, there are three forms for a for statement:
- a single conditional expression
- the three statement version giving an init statement, condition and post statement
- a range clause.
Your statement doesn't match any of these. Most likely the compiler has decided that you are using (1), and errors out when there isn't a { after arrayPointer >= 0. You can fix this by changing to case (2):
for ; arrayPointer >= 0 ; arrayPointer-- {
(or using the arrayPointer initialisation statement as the first part of the for statement).
答案2
得分: 1
这段代码除了 for 语句的错误之外还有一些其他错误（例如，你的 arrayPointer 被初始化为 len(argString) 而不是 len(argString)-1，所以你会立即遇到越界违规）。
无论如何，我认为这是你尝试的一个优化的、惯用的版本：
package mainimport "fmt"func main() {inString := "I am a string"// 使用一个输出缓冲区，因为（1）字符串是不可变的，// （2）向字符串追加会从现有字符串和新追加的部分创建一个新字符串。// 这种方法一次性分配了所有必要的内存。// len(inString) 次分配 vs 1 次分配。outBuffer := make([]uint8, len(inString))for i := 0; i < len(outBuffer); i++ {// 将字符串的倒数第 i 个字符复制到 outBuffer 的第 i 个位置outBuffer[i] = inString[len(inString)-i-1]}fmt.Println(string(outBuffer))}
希望对你有帮助！
英文:
This code has a few errors besides the malformed for statement (e.g., your arrayPointer is initialized to len(argString) rather than len(argString)-1, so you'll hit an out-of-bounds violation right away).
Anyway, I think this an optimized, idiomatic version of what you're attempting:
http://play.golang.org/p/fFCf3L8ov9
package mainimport "fmt"func main() {inString := "I am a string"// use an output buffer because (1) strings are immutable and// (2) appending to strings creates a new string from the existing// string and its new appendix. This method allocates// all the necessary memory 1 time. len(inString) allocations// vs 1 allocation.outBuffer := make([]uint8, len(inString))for i := 0; i < len(outBuffer); i++ {// copy the i-th character from the end of the string// into the i-th position of outBufferoutBuffer[i] = inString[len(inString)-i-1]}fmt.Println(string(outBuffer))}
通过集体智慧和协作来改善编程学习和解决问题的方式。致力于成为全球开发者共同参与的知识库，让每个人都能够通过互相帮助和分享经验来进步。
评论