Separate string and char

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I have, for example:
1 height<200.0
or
1 height< 200.0
using

int index;
std::string attribute;    //these variable types are set and I cannot change them
char opr;
double value;
while(file>>index>>attribute>>opr>>value){...

I want attribute="height", opr='<' and value=200.0. I later load those values into an unordered_map, but that's not my concern.

My problem is, whenever the operator (in that case '<') adheres the attribute string, those values dont get loaded correctly. I want to somehow separate the attribute string and the opr char.

What I have tried:

I've tried inserting a space (" ") to the attribute string, but then, char would be equal to '2', taken from 200.0.
I've also thought about setting opr to '<', but then the value would simply be 00.0, because I replaced the 2 with the <.

Posted 4-Jan-21 7:58am

lelor

Updated 4-Jan-21 9:26am

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Rick York 4-Jan-21 15:12pm

It's not clear what your question really is. Are you asking about reading the file or writing the file?

lelor 4-Jan-21 15:54pm

I am trying to read the file and then load it into an unordered_map. The problem is with reading, sorry if there's a wording problem

Richard MacCutchan 4-Jan-21 15:52pm

the text height<200.0 is a single string and so will be passed into the attribute field. You need to write your own text parser.

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k5054 · Answer 1 · 2021-01-04T09:26:00

You probably need to read the input as a single line then parse it youself. You have:

C++

while(file>>index>>attribute>>opr>>value){...

since attribute is of type string, file>>attribute will read up to the next delimiter character, which is normally a char of type space e.g. space, tab, new-line, etc. If your input is

1 height<200.0
2 width<400.0
3 depth<150.0

then, on the first read:

index = 1
attribute = "height<200.0"
opr = '2'
value = 0.0

and the file input pointer will be at the beginning of 'width' on line 2. The next attempt to read will fail to read in anything, since 'w' is not a digit, and cannot be converted to an int.
You can use getline() to read in a single line from the file, then, depending on how complex the input strings might possibly get, break down your input string, perhaps with find_first_of() or find_first_not_of or maybe look into regex classes to help parse the string.