c - Strace with writev() function in Linux, what does the '@', '2w', and '240K' represent in the data? -



c - Strace with writev() function in Linux, what does the '@', '2w', and '240K' represent in the data? -

i have strace of programme interacts usb, , wondering next write command tells me. understand writev iovec construction consists of info array pointer followed length, "@\10\335 \320\2w\4\240k\252\0\7" in info array denote? i'm particularly wondering @ symbol, 2w, , 240k means not hex info values expect them be.

i'm running on linux , here writev line:

writev(6, [{"@\10\335 \320\2w\4\240k\252\0\7", 13}, {"\0\0\0\4\0\0\0\4", 8}], 2) = 21

from man page of writev:

ssize_t readv(int fd, const struct iovec *iov, int iovcnt);

that is, sec argument array of size value of 3rd argument (2 in case) elements of type struct iovec.

when strace prints octal escapes unprintable characters displays other can printed. hence, @ byte corresponding @, k byte corresponding k , on.

answering questions in comment, @ man page shows

struct iovec { void *iov_base; /* starting address */ size_t iov_len; /* number of bytes transfer */ };

which means {"@\10\335 \320\2w\4\240k\252\0\7", 13} read iov_len = 13 , iov_base memory area containing bytes printed @\10\335 \320\2w\4\240k\252\0\7. fire gdb if want see binary values:

[mihai@winterfell 1]$ gdb -q (gdb) p/x "@\10\335 \320\2w\4\240k\252\0\7" $1 = {0x40, 0x8, 0xdd, 0x20, 0xd0, 0x2, 0x77, 0x4, 0xa0, 0x4b, 0xaa, 0x0, 0x7, 0x0}

where lastly 0x0 null terminator of string , should ignored.

c linux strace

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