Question

我目前正在编写一个C ++应用程序，它与math.h一起实现了一个振荡器。我的代码应该适用于应用程序（尝试编译目标文件），我得到的编译器错误很可能与语法/等有关;我认为这与命名空间有关。错误：

终端输出：

User-Name-Macbook-Pro:Synth Parts UserName$ make
g++ -o Oscillators.o -c -I. Oscillators.cpp -c
In file included from Oscillators.cpp:2:
/usr/include/math.h:41: error: expected unqualified-id before string constant
In file included from /usr/include/c++/4.2.1/bits/locale_facets.tcc:42,
             from /usr/include/c++/4.2.1/locale:46,
             from /usr/include/c++/4.2.1/bits/ostream.tcc:46,
             from /usr/include/c++/4.2.1/ostream:635,
             from /usr/include/c++/4.2.1/iostream:45,
             from Oscillators.cpp:4:
/usr/include/c++/4.2.1/typeinfo:41: error: expected declaration before end of line
make: *** [Oscillators.o] Error 1

Oscillators.cpp

#include "Oscillators.h"
#include <math.h>
#include <vector>
#include <iostream>

#define TWOPI (6.2831853072)

using namespace std;

oscillator(int srate = 44100, int tabsize = 8192, double freq = 200) // Default to output 200Hz Sine Wave
{
    if(srate <= 0) {
        cout << "Error: sample rate must be positive" << endl;
        return;
    }
    sizeovrsr_ = (double)tabsize / (double)srate
    if(freq < 20 || freq > 20000) {
        cout << "Error: frequency is out of audible range" << endl;
        return;
    }
    curfreq_ = freq;
    curphase_ = 0.0 // Not out of one, out of tabsize
    incr_ = curfreq * sizeovrsr_;
    for(int i = 0; i < tabsize; i++) {
        gtable.push_back(sin((i*TWOPI)/(double)tabsize));
    }
    gtable.push_back(gtable[0]);
}

void print_table()
{
    vector<double>::size_type i;
    for(i = 0; i < gtable.size(); i++)
        cout << gtable[i] << "\n";
    cout << endl;
}

Oscillators.h

#ifndef GUARD_OSCILLATORS_H
#define GUARD_OSCILLATORS_H
#include <vector>

class oscillator {
public:
    /*
    void fill_sine(); // Will change the table to a sine wave
    void fill_square(); // Will change the table to a square wave
    void fill_sawtooth(); // Will change the table to a sawtooth wave
    void fill_triangle(); // Will change the table to a triangle wave
    double tick(double freq); // Will output the current sample and update the phase
    */
    void print_table(); // Will print all table values to standard output
    oscillator(int srate = 44100, double freq = 200, int tabsize = 8192);
private:
    double sizeovrsr_; // Will be set at initialization and will determine phase increase for tick func
    double curphase_;
    double curfreq_; // if the freq sent to a tick function doesn't match the current tick, it will be reset;
    double incr_;
    std::vector<double> gtable_; // Will contain a wavetable with a guard point.
}
#endif

我见过其他提到使用g ++ -Wall -g的建议，但我不确定那是不是问题，而且这里还有其他的东西。

任何帮助将不胜感激！谢谢！

Answer 1

这是一个简单的问题。

您刚忘记了头文件末尾的半冒号。

在类定义结尾处错过半冒号所得到的编译器错误很难与实际问题相关 - 只是习惯在创建类后出现错误时检查它。

Answer 2

产生此错误的另一种方法：将宏定义为字符串常量，然后使用宏名称作为字符串常量的名称。实施例

#define FOO "bar"
static const char FOO[] = "bar"; // <-- Error "expected unqualified-id before string constant".

显而易见的答案是删除其中一个定义，或更改其中一个名称。

Answer 3

您的代码有多个问题：

您需要在oscillators.cpp中完全限定名称（void oscillators::print_table()而非void print_table()）
您可能需要#include "oscillators.h"进入oscillators.cpp
您需要在实施中正确声明变量
添加缺少的分号。

但我猜特定错误是由于头文件中的类定义后缺少分号引起的。只需添加它：

    std::vector<double> gtable_; // Will contain a wavetable with a guard point.
};
#endif

字符串常量之前的预期unqualified-id

3 个答案: