当给定A_folder 和file_1 时，您需要一个帮助函数来构造您需要的路径A_folder/file_1。
这种函数的一个典型例子是
char *combine_path(const char *dir, const char *name)
{
/* Calculate the lengths of the path components.
If the respective parameter is NULL, the length is zero .*/
const size_t dirlen = (dir) ? strlen(dir) : 0;
const size_t namelen = (name) ? strlen(name) : 0;
char *path, *p;
/* We allocate <dir> + '/' + <name> + '\0'. */
path = malloc(dirlen + namelen + 2);
if (!path) {
errno = ENOMEM;
return NULL;
}
/* Let p point to the current position in the
resulting path. */
p = path;
/* If there is a directory part,
copy it, and append a '/' after it. */
if (dirlen > 0) {
memcpy(p, dir, dirlen);
p += dirlen;
*p = '/';
p += 1;
}
/* If there is a name part, copy it. */
if (namelen > 0) {
memcpy(p, name, namelen);
p += namelen;
}
/* Append a NUL char, '\0', to terminate the
dynamically allocated buffer.
This turns it into a C string. */
*p = '\0';
/* Return the pointer to the dynamically-allocated
memory, containing the concatenated paths
as a single string. */
return path;
}
请注意，上述函数返回一个动态分配的副本，因此当您不再需要该结果时，您应该free()。
我更喜欢更明确的错误检查。考虑：
int copy_file(const char *frompath, const char *topath)
{
struct stat frominfo, toinfo;
char data[BUFFERSIZE];
ssize_t n;
int src, dst, cause;
if (!frompath || !*frompath ||
!*topath || !*topath) {
fprintf(stderr, "copy_file(): NULL or empty file name!\n");
return errno = EINVAL;
}
src = open(frompath, O_RDONLY | O_NOCTTY);
if (src == -1) {
cause = errno;
fprintf(stderr, "%s: Cannot open file: %s.\n", frompath, strerror(cause));
return errno = cause;
}
if (fstat(src, &frominfo) == -1) {
cause = errno;
fprintf(stderr, "%s: Cannot get file statistics: %s.\n", frompath, strerror(cause));
return errno = cause;
}
dst = open(topath, O_WRONLY | O_CREAT | O_EXCL, frominfo.st_mode & 0777);
if (dst == -1) {
cause = errno;
fprintf(stderr, "%s: Cannot create file: %s.\n", topath, strerror(saved_errno));
errno = cause;
}
while (1) {
char *p, *q;
n = read(src, buffer, sizeof buffer);
if (n == 0) {
/* End of input. */
cause = 0;
break;
} else
if (n < 0) {
/* Error (or interrupt, EINTR). */
if (n == -1)
cause = errno;
else
cause = EIO; /* n < -1 is a bug. */
fprintf(stderr, "%s: Read error: %s.\ņ", frompath, strerror(cause));
break;
}
p = buffer;
q = n;
cause = 0;
while (p < q) {
n = write(dst, p, (size_t)(q - p));
if (n > 0)
p += n;
else
if (n == -1) {
cause = errno;
break;
else {
/* Bug; should never occur. */
cause = EIO;
break;
}
}
if (cause) {
fprintf(stderr, "%s: Write error: %s.\n", topath, strerror(cause));
break;
}
}
/* Failed? */
if (cause) {
unlink(topath);
return errno = cause;
}
if (fstat(dst, &toinfo) == -1) {
cause = errno;
fprintf(stderr, "%s: Cannot get file information: %s.\n", topath, strerror(cause));
unlink(topath);
return errno = cause;
}
/* from may be a device; if so, its size
will be zero. */
if (frominfo.st_size > 0 &&
frominfo.st_size != toinfo.st_size) {
cause = EIO;
fprintf(stderr, "%s: File size mismatch!\n", topath);
unlink(topath);
return errno = cause;
}
/* Careful closing. */
if (close(src) == -1) {
cause = errno;
fprintf(stderr, "%s: Error closing file: %s.\n", frompath, strerror(cause));
unlink(topath);
return errno = cause;
}
if (close(dst) == -1) {
cause = errno;
fprintf(stderr, "%s: Error closing file: %s.\n", topath, strerror(cause));
unlink(topath);
return errno = cause;
}
/* Success. */
return errno = 0;
}
请注意我如何使用p 和q 指针将读取缓冲区内容写入可能不止一个部分的模式。如果源文件是本地文件，而目标文件位于某个不稳定的文件系统上，则可能会发生这种情况。 要求write() 应该写入整个缓冲区或返回错误代码；短写（仅写入给定缓冲区中的一些初始数据）完全可以，并且在某些情况下确实会发生。以上是我首选的处理方式。
许多人认为这种级别的错误检查 - 尤其是检查 close() 的结果值，因为此时许多操作系统（包括 Linux）从不返回错误 - 愚蠢或至少偏执。
我个人认为这种错误检查“稳健”，因为我希望我的代码告诉我，作为用户，如果发生了任何不愉快的事情；我绝对不希望它只是假设一切都很好，我希望它对此感到偏执。 （我并不是说 OP 的代码不检查错误代码；我只是说这个版本更加谨慎和直言不讳。）