When manually generating a JSON object or array, it's often easier to leave a trailing comma on the last item in the object or array. For example, code to output from an array of strings might look like (in a C++ like pseudocode):
s.append("[");
for (i = 0; i < 5; ++i) {
s.appendF("\"%d\",", i);
}
s.append("]");
giving you a string like
[0,1,2,3,4,5,]
Is this allowed?
Unfortunately the JSON specification does not allow a trailing comma. There are a few browsers that will allow it, but generally you need to worry about all browsers.
In general I try turn the problem around, and add the comma before the actual value, so you end up with code that looks like this:
s.append("[");
for (i = 0; i < 5; ++i) {
if (i) s.append(","); // add the comma only if this isn't the first entry
s.appendF("\"%d\"", i);
}
s.append("]");
That extra one line of code in your for loop is hardly expensive...
Another alternative I've used when output a structure to JSON from a dictionary of some form is to always append a comma after each entry (as you are doing above) and then add a dummy entry at the end that has not trailing comma (but that is just lazy ;->).
Doesn't work well with an array unfortunately.
No. The JSON spec, as maintained at http://json.org, does not allow trailing commas. From what I've seen, some parsers may silently allow them when reading a JSON string, while others will throw errors. For interoperability, you shouldn't include it.
The code above could be restructured, either to remove the trailing comma when adding the array terminator or to add the comma before items, skipping that for the first one.
Simple, cheap, easy to read, and always works regardless of the specs.
$delimiter = '';
for .... {
print $delimiter.$whatever
$delimiter = ',';
}
The redundant assignment to $delim is a very small price to pay.
Also works just as well if there is no explicit loop but separate code fragments.
Trailing commas are allowed in JavaScript, but don't work in IE. Douglas Crockford's versionless JSON spec didn't allow them, and because it was versionless this wasn't supposed to change. The ES5 JSON spec allowed them as an extension, but Crockford's RFC 4627 didn't, and ES5 reverted to disallowing them. Firefox followed suit. Internet Explorer is why we can't have nice things.
As it's been already said, JSON spec (based on ECMAScript 3) doesn't allow trailing comma. ES >= 5 allows it, so you can actually use that notation in pure JS. It's been argued about, and some parsers did support it (http://bolinfest.com/essays/json.html, http://whereswalden.com/2010/09/08/spidermonkey-json-change-trailing-commas-no-longer-accepted/), but it's the spec fact (as shown on http://json.org/) that it shouldn't work in JSON. That thing said...
... I'm wondering why no-one pointed out that you can actually split the loop at 0th iteration and use leading comma instead of trailing one to get rid of the comparison code smell and any actual performance overhead in the loop, resulting in a code that's actually shorter, simpler and faster (due to no branching/conditionals in the loop) than other solutions proposed.
E.g. (in a C-style pseudocode similar to OP's proposed code):
s.append("[");
// MAX == 5 here. if it's constant, you can inline it below and get rid of the comparison
if ( MAX > 0 ) {
s.appendF("\"%d\"", 0); // 0-th iteration
for( int i = 1; i < MAX; ++i ) {
s.appendF(",\"%d\"", i); // i-th iteration
}
}
s.append("]");
PHP coders may want to check out implode(). This takes an array joins it up using a string.
From the docs...
$array = array('lastname', 'email', 'phone');
echo implode(",", $array); // lastname,email,phone
Interestingly, both C & C++ (and I think C#, but I'm not sure) specifically allow the trailing comma -- for exactly the reason given: It make programmaticly generating lists much easier. Not sure why JavaScript didn't follow their lead.
Rather than engage in a debating club, I would adhere to the principle of Defensive Programming by combining both simple techniques in order to simplify interfacing with others:
As a developer of an app that receives json data, I'd be relaxed and allow the trailing comma.
When developing an app that writes json, I'd be strict and use one of the clever techniques of the other answers to only add commas between items and avoid the trailing comma.
There are bigger problems to be solved...
Use JSON5. Don't use JSON.
Objects and arrays can have trailing commas
Object keys can be unquoted if they're valid identifiers
Strings can be single-quoted
Strings can be split across multiple lines
Numbers can be hexadecimal (base 16)
Numbers can begin or end with a (leading or trailing) decimal point.
Numbers can include Infinity and -Infinity.
Numbers can begin with an explicit plus (+) sign.
Both inline (single-line) and block (multi-line) comments are allowed.
http://json5.org/
https://github.com/aseemk/json5
No. The "railroad diagrams" in https://json.org are an exact translation of the spec and make it clear a , always comes before a value, never directly before ]:
or }:
There is a possible way to avoid a if-branch in the loop.
s.append("[ "); // there is a space after the left bracket
for (i = 0; i < 5; ++i) {
s.appendF("\"%d\",", i); // always add comma
}
s.back() = ']'; // modify last comma (or the space) to right bracket
According to the Class JSONArray specification:
An extra , (comma) may appear just before the closing bracket.
The null value will be inserted when there is , (comma) elision.
So, as I understand it, it should be allowed to write:
[0,1,2,3,4,5,]
But it could happen that some parsers will return the 7 as item count (like IE8 as Daniel Earwicker pointed out) instead of the expected 6.
Edited:
I found this JSON Validator that validates a JSON string against RFC 4627 (The application/json media type for JavaScript Object Notation) and against the JavaScript language specification. Actually here an array with a trailing comma is considered valid just for JavaScript and not for the RFC 4627 specification.
However, in the RFC 4627 specification is stated that:
2.3. Arrays
An array structure is represented as square brackets surrounding zero
or more values (or elements). Elements are separated by commas.
array = begin-array [ value *( value-separator value ) ] end-array
To me this is again an interpretation problem. If you write that Elements are separated by commas (without stating something about special cases, like the last element), it could be understood in both ways.
P.S. RFC 4627 isn't a standard (as explicitly stated), and is already obsolited by RFC 7159 (which is a proposed standard) RFC 7159
It is not recommended, but you can still do something like this to parse it.
jsonStr = '[0,1,2,3,4,5,]';
let data;
eval('data = ' + jsonStr);
console.log(data)
With Relaxed JSON, you can have trailing commas, or just leave the commas out. They are optional.
There is no reason at all commas need to be present to parse a JSON-like document.
Take a look at the Relaxed JSON spec and you will see how 'noisy' the original JSON spec is. Way too many commas and quotes...
http://www.relaxedjson.org
You can also try out your example using this online RJSON parser and see it get parsed correctly.
http://www.relaxedjson.org/docs/converter.html?source=%5B0%2C1%2C2%2C3%2C4%2C5%2C%5D
As stated it is not allowed. But in JavaScript this is:
var a = Array()
for(let i=1; i<=5; i++) {
a.push(i)
}
var s = "[" + a.join(",") + "]"
(works fine in Firefox, Chrome, Edge, IE11, and without the let in IE9, 8, 7, 5)
From my past experience, I found that different browsers deal with trailing commas in JSON differently.
Both Firefox and Chrome handles it just fine. But IE (All versions) seems to break. I mean really break and stop reading the rest of the script.
Keeping that in mind, and also the fact that it's always nice to write compliant code, I suggest spending the extra effort of making sure that there's no trailing comma.
:)
I keep a current count and compare it to a total count. If the current count is less than the total count, I display the comma.
May not work if you don't have a total count prior to executing the JSON generation.
Then again, if your using PHP 5.2.0 or better, you can just format your response using the JSON API built in.
Since a for-loop is used to iterate over an array, or similar iterable data structure, we can use the length of the array as shown,
awk -v header="FirstName,LastName,DOB" '
BEGIN {
FS = ",";
print("[");
columns = split(header, column_names, ",");
}
{ print(" {");
for (i = 1; i < columns; i++) {
printf(" \"%s\":\"%s\",\n", column_names[i], $(i));
}
printf(" \"%s\":\"%s\"\n", column_names[i], $(i));
print(" }");
}
END { print("]"); } ' datafile.txt
With datafile.txt containing,
Angela,Baker,2010-05-23
Betty,Crockett,1990-12-07
David,Done,2003-10-31
String l = "[" + List<int>.generate(5, (i) => i + 1).join(",") + "]";
Using a trailing comma is not allowed for json. A solution I like, which you could do if you're not writing for an external recipient but for your own project, is to just strip (or replace by whitespace) the trailing comma on the receiving end before feeding it to the json parser. I do this for the trailing comma in the outermost json object. The convenient thing is then if you add an object at the end, you don't have to add a comma to the now second last object. This also makes for cleaner diffs if your config file is in a version control system, since it will only show the lines of the stuff you actually added.
char* str = readFile("myConfig.json");
char* chr = strrchr(str, '}') - 1;
int i = 0;
while( chr[i] == ' ' || chr[i] == '\n' ){
i--;
}
if( chr[i] == ',' ) chr[i] = ' ';
JsonParser parser;
parser.parse(str);
I usually loop over the array and attach a comma after every entry in the string. After the loop I delete the last comma again.
Maybe not the best way, but less expensive than checking every time if it's the last object in the loop I guess.
This question already has answers here:
Is there an equivalent of PHP's mysql_real_escape_string() for Perl's DBI?
(5 answers)
Closed 9 years ago.
I've a set of elements in an array which is read from a file.Now i want to use this array value in sql statement in in Claus!for that i need to enclose these string by '(single quote).so I've tried with for loop to do this! is there any way to do this same opp? like any in build functions like qw...
code:
open FILE, "<tab_name.txt" or die $!;
my #tab=<FILE>;
chomp(#tab);
#tab=split(",",$tab[0]);#set of like eg:$tab[0]=asc,cdf,sad,casd,aea,aee,asdf
my #sql_str=();
foreach my $item(#tab){
$item="'".$item."'";
push(#sql_str,$item);#add comma
push(#sql_str,",");
}
pop(#sql_str);#remove lase unwanted comma
i got the desired output like 'asc','cdf','sad','casd','aea','aee','asdf'
but is there any way to do this?
Do You need an array, or a string fr the in clasue? I assume a string is proper, so what about this?
my $sql_str = join ",", map { $dbh->quote $_ } split ",", $tab[0];
But Miguel Prz is right, You should use parameter binding instead! This will save Your Oracle server for parsing over and over again the same SQL statements.
Other minor issue. If You use my #tab=<FILE>; it will read the whole file. But in the code only the first line is used. So You could use my $tab = <FILE>; to read only the first line.
To do this with placeholders (i.e., properly), you need to first gather all the values for the IN clause into a single array (#values) so that you know how many of them there are, then:
my $in_clause = join(', ', ('?') x scalar #values);
my $sql_str = "select field1, field2 from my_table where id in ( $in_clause )";
my $sth = $dbh->prepare($sql_str);
$sth->execute(#values);
(scalar isn't strictly necessary here, but included to make it a little more obvious what's going on for the OP.)
This may works:
my $sql_str = join ',' => map { $_ = qq|'$_'|; } #tab;
But, manually building your SQL this way is a bad idea. Parameter binding is the proper way to solve this problem.
i know this seems to be a stupid question, but i'm really getting trouble here.
I'm working in a project where i have some functions i can´t modify. That is, i got some C functions (not really my speciality) inside my Obj. C code that i can modify.
So here it is... to explain a little what i have.
I'm receiving a NSData like "\xce\x2d\x1e\x08\x08\xff\x7f" . I have to put each \hex code in a char array, like this:
cArray[1]=ce;
cArray[2]=2d;
cArray[3]=1e;
cArray[4]=08;
etc, etc... of course not LIKE THIS, but just so you understand. My initial move was to separe the NSData with subdataWithRange: and fill in an array with all "subdata". So the next move could be passing each position of that array to a char array, and that's where i got stuck.
I'm using something like (dont have my code right now)
for(int i=0 ; i<=64 ; i++) {
[[arrayOfSubData objectAtIndex:i] getBytes:&charArray[i]];
}
To fill the char array with the hex from my array of subData. That works almost perfectly. Almost.
Taking that example of cArray, my NSLog(#"pos%i: %x",i,charArray[i]) would show me:
pos1: ce
pos2: 2d
pos3: 1e
pos4: 8
And all the "left zeros" are supressed in that same way. My workaround for the moment (and i´m not sure if it is the best practice here) is to take my subDataArray and initWithFormat: a string with it. With that i can transform the string to an int with NSScanner scanHexInt:, but then i´m stucked again when converting back my decimal int to a hexadecimal CHAR. What would be the best approach to fill my char array that way?
Any help or some "tough love" will be greatly appreciated. Thanks
According to the normal rules of printf formatting (which NSLog follows also) you want the following:
NSLog(#"pos%i: %02x", i, charArray[i]);
The '0' says to left pad with 0s and is a flag. The '2' says to ensure that output for that field is at least two characters. So that'll ensure that at least two characters are output and pad to the left with '0's in order to fill space.
having a bit of trouble finding a solution to this.
I want to take a large ordered text file of words and create - in the same order - a text file of fixed length numeric values.
For example:
Input File Output File
AAA -> 00000001
AAH -> 00002718
AAZ -> 71827651
Initially it seemed a hash function would do the trick. However they are one way. Also perhaps they are a bit "heavyweight" for this. After all, I don't need any cryptography. Plus, it's a reference file. It will never change.
Any compression is a bonus not essential. That said, I don't want the file to get any bigger than it already is. Which is why I don't just want to write out the words as text but with fixed lengths.
So, bottom line; input is a NSString of variable length, output is an integer of fixed length. And, I must be able to take the integer and figure out the string.
Any help much appreciated!
Thanks!
xj
Well, this would be a bit of a brute force method, but here's my guess.
Start by making a custom function to convert one letter of text to an integer less than 100. (I'm not sure if such a function already exists, if so then great!) You might need to just go to stuff like "if ([input isEqual: #"a"]){ return 1;}
Then, run that function on each letter of text, and get the final integer by combining the previous results.
For example:
int myVal1 = [intConverter firstLetter];
int myVal2 = [intConverter secondLetter];
int myVal3 = [intConverter thirdLetter];
int finalValue =100^3 + 100^2*myVal1 + 100*myVal2 + myVal3;
Then, finalValue would be of the form 1(myVal1)(myVal2)(myVal3), which is what I think you're looking for.
To get back the original string, simply use the mod (%) and division functions to get the individual values back, then run the intConverter function backwards. (This would probably mean writing a new function that basically runs those if statements in reverse, but oh well.)
I hope this helps.