fread()，fwrite()函数

fread(buf,size,nmemb,fp):　　从fp中将nmemb个size字节的内容读入到buf缓冲区中。如果没遇到文件结尾，其返回值应等于nmemb，否则返回实际读取的大小。

fwrite(buf,size,nmemb,fp);　　将buf缓冲区中读取的nmemb个size字节的内容写入fp中。返回成功写入的项目数，正常情况下应等于nmemb,若写入发生错误，其返回值小于nmemb.

自定义缓存大小：

void copyFile(char* src, char* dst)
{
    enum{SIZE = 4096};
    FILE *in, *out;
    char buf[SIZE];
    long inCount = 0;
    if ((in = fopen(src, "rb")) == NULL) {
        printf("fail to open source file %s\n", src);
        exit(EXIT_FAILURE);
    }
    if ((out = fopen(dst, "wb")) == NULL) {
        printf("fail to open destination file %s\n", dst);
        exit(EXIT_FAILURE);
    }
    while ((inCount = fread(buf, sizeof(char), SIZE, in)) > 0)
    {
        fwrite(buf, sizeof(char), inCount, out);
    }
    fclose(in);
    fclose(out);
}

 完全缓存：

void copyFull(char* src, char* dst)
{
    FILE *in, *out;
    char *buf;
    
    if ((in = fopen(src, "rb")) == NULL) {
        printf("fail to open source file %s\n", src);
        exit(EXIT_FAILURE);
    }
    if ((out = fopen(dst, "wb")) == NULL) {
        printf("fail to open destination file %s\n", dst);
        exit(EXIT_FAILURE);
    }
    fseek(in, 0, SEEK_END);
    long size = ftell(in);
    buf = (char*)malloc(size);
    rewind(in);
    long len = fread(buf, sizeof(char), size, in);
    if (len == size)
        printf("success load cache\n");
    long len2 = fwrite(buf, sizeof(char), len, out);
    if (len2 == len)
        printf("success copy file\n");
    delete buf;
    fclose(in);
    fclose(out);
}