concatenation

问题 I'm looking at a large database of 1s and 0s with named columns, like this: red blue green orange purple ────── ────── ────── ────── ────── 0 0 1 0 1 0 1 0 0 0 I want to concatenate all the headings (by row) where the row has a "1" below that heading. So ideally the first one would equal "green, purple" and the second would just read "blue". I have a large amount of data so anything with nesting of a hundred "IF" functions doesn't make sense. I've tried =IF(B1:B5=1, CONCATENATE(A1:A5), "")

问题 I haven't seen anything here or on MDN. I'm sure I'm just missing something. There's got to be some documentation on this somewhere? Functionally, it looks like it allows you to nest a variable inside a string without doing concatenation using the + operator. I'm looking for documentation on this feature. Example: var string = 'this is a string'; console.log(`Insert a string here: ${string}`); 回答1: You're talking about template literals. They allow for both multiline strings and string

问题 I heard a few people expressing worries about "+" operator in std::string and various workarounds to speed up concatenation. Are any of these really necessary? If so, what is the best way to concatenate strings in C++? 回答1: The extra work is probably not worth it, unless you really really need efficiency. You probably will have much better efficiency simply by using operator += instead. Now after that disclaimer, I will answer your actual question... The efficiency of the STL string class

问题 I have the following code: <?php $a = 1; $b = 2; echo "sum: " . $a + $b; echo "sum: " . ($a + $b); ?> When I execute my code I get: 2 sum: 3 Why does it fail to print the string "sum:" in the first echo? It seems to be fine when the addition is enclosed in parentheses. Is this weird behaviour anywhere documented? 回答1: Both operators the addition + operator and the concatenation . operator have the same operator precedence, but since they are left associative they get evaluated like the

问题 I have the following code: <?php $a = 1; $b = 2; echo "sum: " . $a + $b; echo "sum: " . ($a + $b); ?> When I execute my code I get: 2 sum: 3 Why does it fail to print the string "sum:" in the first echo? It seems to be fine when the addition is enclosed in parentheses. Is this weird behaviour anywhere documented? 回答1: Both operators the addition + operator and the concatenation . operator have the same operator precedence, but since they are left associative they get evaluated like the

问题 In languages like Java and C#, strings are immutable and it can be computationally expensive to build a string one character at a time. In said languages, there are library classes to reduce this cost such as C# System.Text.StringBuilder and Java java.lang.StringBuilder . Does php (4 or 5; I'm interested in both) share this limitation? If so, are there similar solutions to the problem available? 回答1: No, there is no type of stringbuilder class in PHP, since strings are mutable. That being

问题 Suppose I have table in Ms Access with following information: ColumnA ColumnB 1 abc 1 pqr 1 xyz 2 efg 2 hij 3 asd My question is, how can I concatenate the values in the second column to a row value based on the first column. The query results that I want is as follows: ColumnA ColumnB 1 abc, pqr, xyz 2 efg, hij 3 asd I want to achieve this through a query. Can someone help me attain this? 回答1: You need a function to do the concatenation. Microsoft Access condense multiple lines in a table

问题 I have the following values: int a=1; int b=0; int c=2; int d=2; int e=1; How do i concatenate these values so that i end up with a String that is 10221 ; please note that multiplying a by 10000, b by 1000.....and e by 1 will not working since b=0 and therefore i will lose it when i add the values up. 回答1: The easiest (but somewhat dirty) way: String result = "" + a + b + c + d + e Edit: I don't recommend this and agree with Jon's comment. Adding those extra empty strings is probably the best

问题 I faced a problem - I need to use a macro value both as string and as integer. #define RECORDS_PER_PAGE 10 /*... */ #define REQUEST_RECORDS \ "SELECT Fields FROM Table WHERE Conditions" \ " OFFSET %d * " #RECORDS_PER_PAGE \ " LIMIT " #RECORDS_PER_PAGE ";" char result_buffer[RECORDS_PER_PAGE][MAX_RECORD_LEN]; /* ...and some more uses of RECORDS_PER_PAGE, elsewhere... */ This fails with a message about "stray #", and even if it worked, I guess I'd get the macro names stringified, not the values

问题 How should I concatenate base64 strings in order to get rid of the "=" characters ? I sent a byte stream[] of data from the servlet as a http response, and at the client side I want to open the pdf viewer. But, I can't view it because of these extra characters. I tried to concatenate with +=, with join, with concat, but I still have the = character at the end of each substring. Maybe if there's a way to concat the strings without the last character. 回答1: The standard base-64 encoding encodes