fread()返回值总是0

[lixiaofeng523]

代码如下：
void main(void)
{
int size = 1;
long n = 0;
int read_size = 0;
char *file_name = "1khz_7s.mp3";//是一个mp3文件
char *buffer = NULL;
FILE *fp;
FILE *stream;


fp = fopen(file_name, "rb");//fopen正确，fp!=NULL
if (NULL == fp)
{
printf("open file:%s falied\n", file_name);
return;
}
fseek(fp, 0, SEEK_END);
n = ftell(fp);
printf("n=%d\n", n);//执行到这时，n=113746，确实是文件的大小，我用UE打开文件数过

buffer = (char *)malloc(n+1);//缓冲区分配正确，buffer的地址不为NULL
if (NULL == buffer)
{
printf("malloc buffer falied and the data doesn't convert\n");
return;
}
printf("buffer address is:0x%08x\n", buffer);
memset(buffer, 0, n+1);
read_size = fread(buffer, 1, n, fp);//此处，read_size的值总是0，为什么？
if (ferror(fp))//检测文件操作是否有错，返回的是0，即不执行下面的printf语句
{
printf("read file:%s falied\n", file_name);
}
printf("read_size=%d\n", read_size);
printf("buffer[0]=0x%02x,buffer[1]=0x%02x\n", buffer[0], buffer[1]);



stream = fopen("mp3.bin", "wb+");
if (stream == NULL)
{
printf("can't open the file mp3.bin or can't create the file");
return;
}
fwrite(buffer, size, n, stream);

free(buffer);
fclose(fp);
fclose(stream);
}

代码的执行过程我已经用注释注明了。哪位能看出是什么问题，小弟不胜感激，谢谢先！

[james_hw]

read_size = fread(buffer, 1, n, fp);//此处，read_size的值总是0，为什么？

前面加一句fseek(fp,0,SEEK_SET);

[james_hw]

ftell把fp指针移动了

[mstlq]

fseek(fp, 0, SEEK_END);之后……
读取的时候忘了fseek(fp, 0, SEEK_SET); 回来……

下面的就好了

#include <iostream>
#include <string>
using namespace std;

int main(void)
{
    int size = 1;
    long n = 0;
    int read_size = 0;
    char *file_name = "1khz_7s.mp3";//是一个mp3文件
    char *buffer = NULL;
    FILE *fp;
    FILE *stream;


    fp = fopen(file_name, "rb");//fopen正确，fp!=NULL
    if (NULL == fp)
    {
        printf("open file:%s falied\n", file_name);
        return 1;
    }
    fseek(fp, 0, SEEK_END);
    n = ftell(fp);
    printf("n=%d\n", n);//执行到这时，n=113746，确实是文件的大小，我用UE打开文件数过

    buffer = (char *)malloc(n+1);//缓冲区分配正确，buffer的地址不为NULL
    if (NULL == buffer)
    {
        printf("malloc buffer falied and the data doesn't convert\n");
        return 1;
    }
    printf("buffer address is:0x%08x\n", buffer);
    memset(buffer, 0, n+1);

    fseek(fp, 0, SEEK_SET);   //将指针重置到文件头……
    read_size = fread(buffer, 1, n, fp);//此处，read_size的值总是0，为什么？
    if (ferror(fp))//检测文件操作是否有错，返回的是0，即不执行下面的printf语句
    {
        printf("read file:%s falied\n", file_name);
    }
    printf("read_size=%d\n", read_size);
    printf("buffer[0]=0x%02x,buffer[1]=0x%02x\n", buffer[0], buffer[1]);


    stream = fopen("mp3.bin", "wb+");
    if (stream == NULL)
    {
        printf("can't open the file mp3.bin or can't create the file");
        return 1;
    }
    fwrite(buffer, size, n, stream);

    free(buffer);
    fclose(fp);
    fclose(stream);
    return 0;
}

[lixiaofeng523]

哦，对，陷入死圈套了，谢谢哥们了。真是笨啊，我！

[deng1243]

正解

[hbvanguard]

fseek(fp, 0, SEEK_END); //在这里你把文件指针指到了文件末尾后面用fread当然读不出来了
:
:
rewind(fp);//fread之前把文件指针重新指回文件头
fread();

[lylm]

fseek(fp, 0, SEEK_END);
LZ这里已经移到末尾了