使用C

Question

有人可以告诉我这段代码中我做错了什么吗？它可以编译，但不能正确反转音频文件。它确实通过不正确地使音频清晰来反转文件类型。这是 cs50x 课程的问题集 4。我相信 TODO #8 有问题。

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

#include "wav.h"

int check_format(WAVHEADER header);
int get_block_size(WAVHEADER header);

int main(int argc, char *argv[])
{
    // Ensure proper usage
    // TODO #1
    if (argc != 3)
    {
        printf("entre input and output file names\n");
        return 1;
    }

    // Open input file for reading
    // TODO #2
    char *infile = argv[1];
    char *outfile = argv[2];

    FILE *inptr = fopen(infile, "r");
    if (inptr == NULL)
    {
        printf("error opening file\n");
        fclose(inptr);
        return 2;
    }

    // Read header
    // TODO #3
    WAVHEADER wv;
    fread(&wv, sizeof(WAVHEADER), 1, inptr);
    long position = ftell(inptr);

    // Use check_format to ensure WAV format
    // TODO #4

    if (check_format(wv) == -1)
    {
        printf("input is not a wav.h file\n");
        fclose(inptr);
        return 3;
    }

    // Open output file for writing
    // TODO #5
    FILE *outptr = fopen(outfile, "wb");
    if (outptr == NULL)
    {
        printf("error opening output file\n");
        fclose(outptr);
        fclose(inptr);
        return 4;
    }

    // Write header to file
    // TODO #6
    fwrite(&wv, sizeof(WAVHEADER), 1, outptr);

    // Use get_block_size to calculate size of block
    // TODO #7
    int blsize = get_block_size(wv);

    // Write reversed audio to file
    // TODO #8
    DWORD bufferSize = wv.subchunk2Size;

    int16_t *audio = malloc(bufferSize);
    fseek(inptr, blsize, SEEK_END);
    fseek(outptr, position, SEEK_SET);

    for (int i = 0; i < bufferSize / blsize; i++)
    {
        fread(&audio[i], blsize, 1, inptr);
        fseek(inptr, (-2) * blsize, SEEK_CUR);

        fwrite(&audio[i], blsize, 1, outptr);
    }

    fclose(outptr);
    fclose(inptr);
    free(audio);
}

int check_format(WAVHEADER header)
{
    // TODO #4
    char elmnts[] = {'W', 'A', 'V', 'E', '\0'};
    for (int i = 0; i < 4; i++)
    {
        if (elmnts[i] != header.format[i])
        {
            return -1;
        }
    }
    return 0;
}

int get_block_size(WAVHEADER header)
{
    // TODO #7
    int blsize = header.numChannels * (header.bitsPerSample / 8);
    return blsize;
}

我不知道该怎么办。请帮忙。

Answer 1

我同意你的怀疑——一个坚实的痛点似乎是 TODO #8 这是一个搜索问题...请尝试这种方法：

// Write reversed audio to file
// TODO #8
DWORD bufferSize = wv.subchunk2Size;
DWORD readPosition;  /* Added readPosition*/

fseek(inptr, 0, SEEK_END);  /* Seek to EOF */
readPosition = ftell(inptr); /* Set readPosition to EOF*/

int16_t *audio = malloc(bufferSize);
fseek(outptr, position, SEEK_SET);

/* Also please double check this limit -> ( bufferSize / blsize ) 
** (might be fine, not sure) */
for (int i = 0; i < bufferSize / blsize; i++)
{
    readPosition -= blsize;  /* Decrement readPosition by block size*/
    fseek(inptr, readPosition, SEEK_SET); /* Seek to read position */

    fread(&audio[i], blsize, 1, inptr);
    fwrite(&audio[i], blsize, 1, outptr);
}