c++ - 为什么使函数 "static"导致我的程序有 undefined symbol ？

Question

我敢肯定， undefined symbol /引用感觉就像是一个在这里被打得死去活来的话题，但我遇到了一个奇怪的问题。看我的previous question了解一些背景信息。

我正在开发一个小程序，它编译正常，没有警告或错误或任何东西。然后，我更新了 CMake，我得到了这些错误:

Undefined symbols for architecture x86_64:
  "std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >::basic_string(char const*)", referenced from:
      GetName() in n2-af52d6.o
      Expression() in n2-af52d6.o
      Term() in n2-af52d6.o
      GetNum() in n2-af52d6.o
  "std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >::basic_string()", referenced from:
      GetName() in n2-af52d6.o
      GetNum() in n2-af52d6.o
  "std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >::operator+=(char)", referenced from:
      GetName() in n2-af52d6.o
      GetNum() in n2-af52d6.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

我认为这很奇怪，因为这些错误似乎来自标准库本身。

这是完整的程序:

//
// ncc.cpp
// Nathanael Epps
//

#include <string>
#include <iostream>
#include <sstream>

typedef std::string string;

static char look = '\0';

static const string Cmt = "## ";
static const string Tab = "\t";
static const string TabTab = Tab + Tab;
static const string TabTabTab = TabTab + Tab;

static void GetChar()
{
    look = getchar();
    while (look == ' ' || look == '\t')
        look = getchar();
}

template <class T>
static string ToString(T x)
{
    std::stringstream ss;
    ss << x;
    return ss.str();
}

static void Error(string mssg)
{
    fprintf(stderr, "\n%s", mssg.c_str());
}

static void Abort(string mssg)
{
    Error(mssg);
    exit(0);
}

static void Expected(string expected)
{
    Abort(expected + " expected.\n");
}

static void Match(char x)
{
    if (x == look)
        GetChar();
    else
        Expected(string("\"") + x + "\"");
}

static bool IsAlpha(char c)
{
    c = toupper(c);
    return 'A' <= c && c <= 'Z';
}

static bool IsDigit(char c)
{
    return '0' <= c && c <= '9';
}

static bool IsAlNum(char c)
{
    return IsAlpha(c) || IsDigit(c);
}

static string GetName()
{
    if (!IsAlpha(look))
        Expected("Alpha");

    std::string name;
    while (IsAlNum(look)) {
        name += look;
        GetChar();
    }

    return name;
}

static string GetNum()
{
    if (!IsDigit(look))
        Expected("Integer");

    string num;
    while (IsDigit(look)) {
        num += look;
        GetChar();
    }

    return num;
}

static void EmitLn(string s)
{
    printf("\t%s\n", s.c_str());
}

static void EmitLn(char c)
{
    printf("\t%c\n", c);
}

static void WriteLn(string s)
{
    printf("%s\n", s.c_str());
}

static void Init()
{
    GetChar();
}

static void Identifier()
{
    auto name = GetName();
    if (look == '(')
    {
        Match('(');
        Match(')');
        EmitLn("movq" + Tab + "$0, %rax");
        EmitLn("callq" + Tab + "_" + name + TabTab + Cmt + "Leaves result in %rax");
    }
    else
    {
        EmitLn("movq" + Tab + name + "(%rip), %rax");
    }
}

static void Expression();

static void Factor()
{
    if (look == '(')
    {
        Match('(');
        Expression();
        Match(')');
    }
    else if (IsAlpha(look))
    {
        Identifier();
    }
    else
    {
        EmitLn("movq" + Tab + "$" + GetNum() + ", %rax");
    }
}

static void Multiply()
{
    Match('*');
    Factor();

    EmitLn("popq" + Tab + "%rbx");
    EmitLn("imulq" + Tab + "%rbx, %rax");
    EmitLn("movq" + Tab + "$0, %rdx");
}

static void Divide()
{
    Match('/');
    Factor();

    // Right now, stack has top number
    // %rax has bottom number

    // move the bottom number to %rbx
    EmitLn("movq" + Tab + "%rax, %rbx");

    // move the top number to %rdx:%rax
    EmitLn("popq" + Tab + "%rax");
    EmitLn("cqto" + TabTabTab + Cmt + "%rax --> %rdx:%rax");

    // do division
    EmitLn("idivq" + Tab + "%rbx");// + TabTab + Cmt + "leaves result in %rax");

    // clear %rdx
    EmitLn("movq" + Tab + "$0, %rdx");// + Tab + Cmt + "clear %rdx");
}

static void Term()
{
    Factor();

    while (look == '*' || look == '/')
    {
        EmitLn("pushq" + Tab + "%rax");

        if (look == '*')
            Multiply();
        else if (look == '/')
            Divide();
        else
            Expected("Mult/Div Op");
    }
}

static void Add()
{
    Match('+');
    Term();
    EmitLn("popq" + Tab + "%rbx");
    EmitLn("addq" + Tab + "%rbx, %rax");
}

static void Sub()
{
    Match('-');
    Term();
    EmitLn("popq" + Tab + "%rbx");
    EmitLn("subq" + Tab + "%rbx, %rax");
    EmitLn("neg " + Tab + "%rax");
}

static bool IsAddop(char c)
{
    return c == '+' || c == '-';
}

static void Expression()
{
    if (IsAddop(look))
        EmitLn("movq" + Tab + "$0, %rax");
    else
        Term();

    while (IsAddop(look))
    {
        EmitLn("pushq" + Tab + "%rax");

        if (look == '+')
            Add();
        else if (look == '-')
            Sub();
        else
            Expected("Add/Sub Op");
    }
}

static void Assignment()
{
    auto name = GetName();

    Match('=');

    Expression();

    //EmitLn("movq" + Tab + "%rax, " + name + "(%rip)");
    EmitLn("movq" + Tab + "%rax, (variable " + name + ")");
}

static string NewLabel()
{
    static unsigned count = 0;
    return "L" + ToString(count++);
}

static void PostLabel(string lname)
{
    WriteLn(lname + ":");
}

static void Condition()
{
    EmitLn("<condition>");
}

static void Other()
{
    EmitLn(look);
    GetChar();
}

static void Block();

static void DoIf()
{
    Match('i');
    string l = NewLabel();
    Condition();
    EmitLn("jne" + Tab + l);
    Block();
    Match('e');
    PostLabel(l);
}

static void Block()
{
    while (look != 'e')
    {
        if (look == 'i')
            DoIf();
        else
            Other();
    }
}

static void Program()
{
    Block();
    if (look != 'e')
        Expected("e");

    EmitLn(Cmt + "Clean up stack, and such");
    EmitLn("retq");

    GetChar();
}

int main()
{
    Init();

    (void) Assignment;

    Program();

    if (look != '\n')
        Expected("Newline");

    return EXIT_SUCCESS;
}

但是，从函数中删除 static 限定符会使错误消失。 (此外，如果您没有弄清楚，该程序是某种小型编译器。)

什么给了？

编辑:

我通常会通过简单地输入链接

g++ ncc.cpp -std=c++14 -Wall -o ncc

运行 g++ --version 得到这个:

Configured with: --prefix=/Applications/Xcode.app/Contents/Developer/usr --with-gxx-include-dir=/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.12.sdk/usr/include/c++/4.2.1
Apple LLVM version 8.0.0 (clang-800.0.42.1)
Target: x86_64-apple-darwin17.6.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin

这个问题不是 this question 的重复问题因为这个答案是关于在文件范围内声明的静态变量导致文件本身中的 undefined symbol ，而我的问题是关于在文件范围内声明的静态函数导致标准库中的 undefined reference 。

Answer 1

C++ 标准库在 Mac 中有两种实现方式，你可以尝试添加这个标志吗？

-stdlib=libstdc++

如果这不起作用，则反过来:

-lstdc++

归功于 this other post .