STL containers for message buffers in socket(-like) communications

I always wondered why custom buffer classes were used in most of our (high performance) libraries. This post made me realize that STL, as extensively used as it is, is not a golden hammer.

C++ Comma Confusion via LightSleeper

Many C++ programmers are surprised by the effects of that little comma. In some cases (e.g. comma operator), the comma very clearly describes the order of operations. In other cases (e.g. function parameter separators), the comma does not describe the order. h() could execute before g() in the last example, and it often does in real compilers. Understanding the difference is well worth your time.

Original Post

awk Search script with prior and following line capability

#!/bin/sh

# *********************************************************

# This uses nawk to list lines coming prior to and after

# the given search string.

# Format: xgrep

# ********************************************************

if [ $# != 4 ]

then

echo "Usage: $0 "

exit

fi

STR=$1

BEF=$2

AFT=$3

while [ ! -z "$4" ] ; do

echo ========== $4

nawk 'c-->0{print NR ":\t" $0;};$0~s{if(b)for(c=b+1;c>1;c--) print (NR-c + 1) ":\t" r[(NR-c+1)%b];print NR ":\t" $0;c=a}b{r[NR%b]=$0;}' b=$BEF a=$AFT s=$STR $4 | sed "s/^/$4\

/"

shift

done

echo ==========

Took me a while to understand how awk worked and customized the command I found on the net for my own needs.

sed and Nix Quotation Confusion

I wanted to use "sed" inside a script to make changes to a text file. The file looked like this:

/*

** Project "OrderCache.7.7.29"

** Hint: deleting everything below the "cause" field will set

** the defaults appropriately for the cause you have chosen.

*/

brief_description = "none";

description = "none";

cause = internal_bug;

test_exempt = true;

test_baseline_exempt = true;

regression_test_exempt = true;

architecture =

[

"unspecified",

];

I wanted to replace the "brief_description" with a value given by the user. So:

#!/bin/csh

set DESC = "$<"

But when I tried to use sed with $DESC:

sed -i 's%brief_description\ \=\ \"none\"\;%brief_description\ \=\ \"$DESC\"\;%g' temp_next.txt

the command would only change "brief_description" as follows:

brief_description = "$DESC";

The reason for this is that the variable has to be inside double quotes in order to get it dereferenced back to the actual value. So the solution is:

sed -i 's%brief_description\ \=\ \"none\"\;%brief_description\ \=\ \"'"$DESC"'\"\;%g' temp_next.txt

posix_spawnp Failure with WEXITSTATUS 127

One problem with posix_spawnp is that if it fails after successfully spawning a new process, the exit status of the spawned process is always 127. This gives us no clue what so ever as to what caused the problem.

I came across this a few days ago and struggled with it for a while before re-writing the code using "fork()" and "execvpe" to achieve the same effect. The "exec" calls also failed but they gave a proper error value (via errno) from which the cause of the error could be found (perror(errno)).

In my case, errno was 14 and the error message said "Bad address" which turned out to be caused by an invalid argument list passed to execvpe. I wasn't terminating the argument list with NULL set as the last element.

Having a better error reporting system in posix_spawnp would have saved me alot of trouble