原题：

编写一个类似 cp 的程序，它复制包含空洞的文件，但不将字节0写到输出文件中去。

源代码：

#include
#include
#include
#include
#include

#define BUF_SIZ 128

int my_cp( const char *file1, const char *file2 )
{
int fd1, fd2;
char buffer[BUF_SIZ];
int res;
int current_position = 0;
int byte_count = 0;

fd1 = open( file1, O_RDWR );
if( -1 == fd1 ) {
perror("open file1 failed");
return -1;
}

fd2 = open( file2, O_RDWR | O_APPEND | O_CREAT | O_TRUNC, 0666 );
if( -1 == fd2 ) {
perror("open file2 failed");
return -1;
}

memset( buffer, '\0', BUF_SIZ );
res = read( fd1, buffer, BUF_SIZ );
if( -1 == res ) {
perror("file1 read error");
return -1;
}

while( 0 != res ) {
byte_count = 0;
for( current_position=0; current_position if( '\0' != buffer[current_position] ) {
buffer[byte_count] = buffer[current_position];
byte_count++;
}
}

res = write( fd2, buffer, byte_count );
if( -1 == res ) {
perror("file2 write failed");
return -1;
}

memset( buffer, '\0', BUF_SIZ );
res = read( fd1, buffer, BUF_SIZ );
if( -1 == res ) {
perror("file1 read failed");
return -1;
}
}
}

int main(int argc, char *argv[])
{
if( 3 != argc) {
printf("correct usage: ./my_cp file1 file2\n");
exit( EXIT_FAILURE );
}

//产生一个含有空洞的文件 file1
int fd = open( argv[1], O_RDWR | O_CREAT | O_TRUNC, 0666 );
if( -1 == fd ) {
perror("open failed");
exit( EXIT_FAILURE );
}

int res = write( fd, "Hey,man!", strlen("Hey,man!") );
if( -1 == res ) {
perror("file1 write failed");
exit( EXIT_FAILURE );
}

off_t offset = lseek( fd, 10000, SEEK_SET );
if( -1 == offset ) {
perror("lseek failed");
exit( EXIT_FAILURE );
}

res = write( fd, "How are you?", strlen("How are you?") );
if( -1 ==res ) {
perror("file1 write failed");
exit( EXIT_FAILURE );
}

//应用 my_cp 函数拷贝文件
res = my_cp( argv[1], argv[2] );
if( -1 == res ) {
perror("copy failed");
exit( EXIT_FAILURE );
}

exit( EXIT_SUCCESS );
}

运行结果：

Hey,man!How are you?

输出文件在本例中为file2，大小为 20 Bytes = strlen("Hey,man!") + strlen("How are you?")。测试通过。

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