Question

I have been reading SO for some time now, but I truly cannot find any help for my problem.

I have a c++ assignment to create an IAS Simulator.

Here is some sample code…

0   1   a
1   2   b
2   c
3   1
10  begin
11  . load a, subtract b and offset by -1 for jump+
11  load M(0)
12  sub M(1)
13  sub M(3)
14  halt

Using c++, I need to be able to read these lines and store them in a “memory register” class that I already have constructed…

For example, the first line would need to store “1 a” in register zero.

How can I parse out the number at the line beginning and then store the rest as a string?

I have setup storage using a class that is called using mem.set(int, string);. int is the memory location at the beginning of the line and string is the stored instruction.

Edit: Some Clarifications:

• I must use standard libraries
• the grammar for the input file is here: http://www.cs.uwyo.edu/~seker/courses/2150/iascode.pdf
• The loader will overwrite duplicate line entries. That means the first line 11 in the sample will be overwritten by the second.

Answer 1

Splitting the leading number and the rest of the line is not too difficult of a task. Use something like getline to read one line at a time from your input file, and store the line in a string char cur_line[]. For each line, try something like this:

• Declare a pointer char* pString and an integer int line_num
• Use the strstr function to find the first whitespace character, and assign the result to pString.
• Move pString forward one character at a time until it points to a non-whitespace character. This is the start of the string containing the “rest of the line”.
• Use atoi on cur_line to convert the first entry in the string to an integer, and store the results in line_num
• Now, you should be able to call your function like mem.set(line_num, pString)

Interpreting those strings is going to be much more difficult, however…

Edit: As Mike DeSimone mentions, you can combine the strstr and atoi steps above if you use one of the strto* functions instead of atoi.