expected unqualified-id before string constant

问题

I'm currently writing a C++ application which implements an Oscillator in conjuction with math.h. The code I have should work fine for the application (trying to compile an object file), bu I'm getting a compiler error most likely having to do with syntax/etc; I think it has something to do with namespace. The error:

Terminal Output:

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

I've seen other suggestions that mention using g++ -Wall -g but I'm not sure that that is the problem, and that there is something else going on here.

Any help would be much appreciated! Thanks!!

回答1:

This is a simple problem.

You just forgot the semi colon at the end of your header file.

The compiler errors you get for missing the semi colon at the end of a class definition are very hard to relate to the actual problem - just get in the habit of checking that when you get errors after you create a class.

回答2:

Another way to produce this error: define a macro to a string constant, and later, use the macro name as the name of a string constant. Example

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

The obvious answer is to remove one of the definitions, or change the name of one.

回答3:

Your code has multiple problems:

You need to fully qualify names(void oscillators::print_table() instead of just void print_table()) in oscillators.cpp
You probably need to #include "oscillators.h" into oscillators.cpp
You need to properly declare variables in implementation
Add missing semicolons.

But I guess that specific error is caused by missing semicolon after class definition in header file. Just add it like:

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

来源：https://stackoverflow.com/questions/11837024/expected-unqualified-id-before-string-constant

标签

c++

namespaces

g++

math.h

object-files