在 C 中使用 scanf() 错误地写入文件

Question

我在编写命令行程序以在计算后写入新文件之前使用文本文件作为输入参数时遇到问题。我当前的程序如下所示：

  /* midi2hzf.c */

/*  Converts midi information files in the format midiNote - midiVelocity - duration(msecs) 
    into a frequency information file formatted frequency - ampFactor - duration(msecs)     */

#include <stdio.h>
#include <math.h>
#include <stdlib.h>

float Hz, ampFat;
int midi, velo, durMidi, durHz;

float calHz(float Hz, int midi){
    Hz = pow(2, ((midi-69)/12))*440;
    return Hz;
    }

float calAmp(float ampFat, int velo){
    if (velo >= 0 && velo <= 127){
        ampFat = velo/127;
        return ampFat;
    }else{
        return 1;
    }
}

int main(int argc, char *argv[]){

    FILE *midiFile;
    midiFile = fopen("testmidi.txt", "r");

    FILE *hzFile;
    hzFile = fopen("testhz.txt", "w");

    if(midiFile==NULL||hzFile==NULL){
        printf("File error\n");
        return 1;
    }else{
        while(!feof(midiFile)){
            fscanf(midiFile, "%d%d%d", &midi,&velo,&durMidi);
            durMidi = durHz;
            calHz(Hz, midi);
            calAmp(ampFat, velo);
            fprintf(hzFile, "%f\t%f\t%d\n", Hz, ampFat, durHz);
            printf("%f\t%f\t%d\n", Hz, ampFat, durHz);
        }
    }

    fclose(hzFile);
    fclose(midiFile);}

每次我运行程序，输出文件都包含“0.0000 0.0000 0”，这显然不是想要的输出。据我所知，我的函数被正确调用并且所有代码都有意义，尽管输出始终是错误的。

Answer 1

您的代码中有很多错误。

#include <stdio.h>
#include <math.h>
#include <stdlib.h>

// Functions don't need an input for their output value.
float calHz(int midi){
    return pow(2, (midi - 69) / 12) * 440;
}

float calAmp(int velo){
    if (velo >= 0 && velo <= 127){
        return velo / 127.0;  // need to divide by floating point value
                              // so we don't just get integer division
    }else{
        return 1;
    }
}

int main(int argc, char *argv[]){

    // Variables should be declared locally.
    float Hz, ampFat;
    int midi, velo, durMidi, durHz;

    FILE *midiFile = fopen("testmidi.txt", "r");
    FILE *hzFile = fopen("testhz.txt", "w");

    if(midiFile==NULL||hzFile==NULL){
        printf("File error\n");
        return 1;
    }else{
        // You need to test the return value of fscanf to control the loop.
        while(fscanf(midiFile, "%d%d%d", &midi, &velo, &durMidi) == 3){
            durHz = durMidi;        // you had this the other way around
            Hz = calHz(midi);       // need to assign return value to Hz
            ampFat = calAmp(velo);  // ditto for ampFat
            fprintf(hzFile, "%f\t%f\t%d\n", Hz, ampFat, durHz);
            printf("%f\t%f\t%d\n", Hz, ampFat, durHz);
        }
    }

    fclose(hzFile);
    fclose(midiFile);
    return 0;
}