C中单个缓冲区中的多个空终止字符串

Question

In need to craft a string with the following format and place it into a single buffer[1000]. Note that \\x00 is the null terminator.

@/foo\x00ACTION=add\x00SUBSYSTEM=block\x00DEVPATH=/devices/platform/goldfish_mmc.0\x00MAJOR=command\x00MINOR=1\x00DEVTYPE=harder\x00PARTN=1

So in essence I need to pack following null terminated strings into a single buffer

@/foo  
ACTION=add  
SUBSYSTEM=block  
DEVPATH=/devices/platform/goldfish_mmc.0  
MAJOR=command  
MINOR=1  
DEVTYPE=harder  
PARTN=1  

How might I go about doing this?

Answer 1

You'll need to copy each string in one at a time, keeping track of where the last copy stopped and starting just after that for the next one.

char *p = buffer;
strcpy(p, "@/foo");
p += strlen(p) + 1;
strcpy(p, "ACTION=add");
p += strlen(p) + 1;
...

Answer 2

You can use %c to print numeric zero with sprintf , like this:

char *a[] = {"quick", "brown", "fox", "jumps"};
int n = 0;
char buf[100];
for (int i = 0 ; i != 4 ; i++) {
    n += sprintf(buf+n, "%s%c", a[i], 0);
}

Demo

Answer 3

You can initialize your buffer with a string containing explicit embedded NUL characters:

char buffer[1000] =
  "@/foo\0"
  "ACTION=add\0"
  "SUBSYSTEM=block\0"  
  "DEVPATH=/devices/platform/goldfish_mmc.0\0"
  "MAJOR=command\0"
  "MINOR=1\0"
  "DEVTYPE=harder\0"  
  "PARTN=1";

Or you can copy it explicitly with memcpy :

char str[] =
  "@/foo\0"
  "ACTION=add\0"
  "SUBSYSTEM=block\0"  
  "DEVPATH=/devices/platform/goldfish_mmc.0\0"
  "MAJOR=command\0"
  "MINOR=1\0"
  "DEVTYPE=harder\0"  
  "PARTN=1";
char buffer[1000];

memcpy(buffer, str, sizeof(str));

Here, the compiler will concatenate adjacent string constants, but only the last string will get an implicit NUL; all others have an explicit NUL.

Also, breaking up a string like "\\01" (which doesn't actually appear in this case) into "\\0" "1" prevents the compiler from seeing the "\\01" as the single character string { 0x01, 0x00 } (with implicit trailing NUL), and instead treats is as the two character string { 0x00, 0x31, 0x00 } (also with an implicit trailing NUL) that was intended.