There many ways to do input\/output in C\/C++. Some are slow, some are fast and some can be very fast. Here I’ll be discussing some of these methods.<\/p>
Many a times during competetive programming you come across the warning “Careful – large input\/output<\/strong>“. Now what exactly does this means? All the code can be found here: GitHub<\/a>.<\/p> First one is the basic method that you guys must already be using. This is based on cin\/cout methods of the iostream library. It is the most basic method and does not require you to specify the type of input you are expecting, but, is extremely slow.<\/p>\n The second method is based on the simple printf\/scanf functions of stdio.h library for C. These are much faster than the above method and can be easily used in competetive programming for a decent time limit. These are multi-thread safe as they lock the file before writing. This method is very fast than the last method and used unlocked <\/strong>versions of the above functions used. I have written the code to scan integer and a string. For others you can easily write your function referring the below code. These are NOT multi-thread safe. Should be used in caution. But, in competetive programming plateforms, one program is already separated from others, so can easilt be used for better I\/O in competetive programming which have even tighter time constraints.<\/p>\n There is another method I came across a solution in one of the problems on codechef<\/a>. I haven’t tested it’s performance, but, his solution had the lowest timing with the same logic for the actual problem. So, I am assuming this gives a better performance for I\/O. You can download the code here<\/a>. I’ll come up with more updates on the same topic.<\/p>\n","protected":false},"excerpt":{"rendered":" There many ways to do input\/output in C\/C++. Some are slow, some are fast and some can be very fast. Here I’ll be discussing some of these methods.Many a times during competetive programming you come across the warning “Careful – large input\/output“. Now what exactly does this means? This basically means that you have to…<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_s2mail":"","footnotes":""},"categories":[38,39],"tags":[13,33,34,35],"class_list":["post-125","post","type-post","status-publish","format-standard","hentry","category-cpp","category-time","tag-c","tag-fast-io","tag-input","tag-output"],"aioseo_notices":[],"_links":{"self":[{"href":"http:\/\/digital-madness.in\/blog\/wp-json\/wp\/v2\/posts\/125","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/digital-madness.in\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/digital-madness.in\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/digital-madness.in\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/digital-madness.in\/blog\/wp-json\/wp\/v2\/comments?post=125"}],"version-history":[{"count":10,"href":"http:\/\/digital-madness.in\/blog\/wp-json\/wp\/v2\/posts\/125\/revisions"}],"predecessor-version":[{"id":200,"href":"http:\/\/digital-madness.in\/blog\/wp-json\/wp\/v2\/posts\/125\/revisions\/200"}],"wp:attachment":[{"href":"http:\/\/digital-madness.in\/blog\/wp-json\/wp\/v2\/media?parent=125"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/digital-madness.in\/blog\/wp-json\/wp\/v2\/categories?post=125"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/digital-madness.in\/blog\/wp-json\/wp\/v2\/tags?post=125"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
\nThis basically means that you have to use an optimized code for your reading\/writing to the standard input\/output to stay inside the tighter time constraints<\/strong> of the problem. So let’s get going and explore the different methods to optimize your I\/O in C\/C++.<\/p>\r\n#include <iostream>\r\n#include <string>\r\n#include <sstream>\r\n\r\nusing namespace std;\r\n\r\nint main() {\r\n\t\/* integer or any integer like *\/\r\n\tint integer;\r\n\t\tcin>>integer;\r\n\t\tcout<<integer<<endl;\r\n\r\n\t\/* character string *\/\r\n\tchar charstring[100];\r\n\t\tcin>>charstring;\t\/\/ stops input after a "space"\r\n\t\tcout<<charstring<<endl;\r\n\r\n\t\tcin.getline(charstring, 100);\t\/\/ stops after 100 character or eof whichever comes first\r\n\t\tcout<<charstring<<endl;\r\n\r\n\tstring strstring;\r\n\t\tcin>>strstring;\t\t\/\/ stops input after a "space"\r\n\t\tcout<<strstring<<endl;\r\n\r\n\t\tgetline(cin, strstring);\t\/\/ stops after eof or '\\n', whichever comes first\r\n\t\tcout<<strstring<<endl;\r\n\r\n\t\/* safest way to get an integer (but very slow) - taken from cpluspls.com *\/\r\n\tint number = 0;\r\n\tstring input;\r\n\twhile(true) {\r\n\t\tgetline(cin, input);\r\n\r\n\t\tstringstream myStream(input);\r\n\t\tif(myStream>>number)\r\n\t\t\tbreak;\r\n\t}\r\n\r\n\t\/* Safest way to get a single character *\/\r\n\tchar singlechar = {0};\r\n\twhile(true) {\r\n\t\tgetline(cin, input);\r\n\r\n\t\tif(input.length() == 1){\r\n\t\t\tsinglechar = input[0];\r\n\t\t\tbreak;\r\n\t\t}\r\n\t}\r\n}\r\n<\/pre>
\nDetailed description of the stdio.h library you can refer to here<\/a>.<\/p>\n\r\n#include <cstdio>\r\n#include <string>\r\n\r\nint main() {\r\n\t\/* integer I\/O *\/\r\n\tint a;\r\n\tscanf("%d", &a);\r\n\tprintf("%d\\n", a);\r\n\r\n\t\/*\r\n Other format specifiers.\r\n %d, %i = signed integer\r\n %u = unsigned integer\r\n %l = prefix for long\r\n %f = signed floating point\r\n %e = signed scientific\r\n %c = single character\r\n\t*\/\r\n\r\n\t\/* sting I\/O *\/\r\n\tchar charstring[100];\r\n\tscanf("%s", charstring); \/\/ only till the first white space is stored\r\n\tprintf("%s\\n", charstring);\r\n\r\n\tscanf("%[^\\n]s", charstring); \/\/ sets th delimeter to be "new line"\r\n\tprintf("%s\\n", charstring); \/\/ thus whole line is read until a \\n is observed\r\n\t\t\t\t\t\t\t\t\/\/ does not eliminate \\n from the input stream\r\n\r\n\tgets(charstring);\r\n\tprintf("%s\\n", charstring);\r\n}\r\n<\/pre>\r\n#include <cstdio>\r\n\r\ninline void fastRead_int(int &x) {\r\n register int c = getchar_unlocked();\r\n x = 0;\r\n int neg = 0;\r\n\r\n for(; ((c<48 || c>57) && c != '-'); c = getchar_unlocked());\r\n\r\n if(c=='-') {\r\n \tneg = 1;\r\n \tc = getchar_unlocked();\r\n }\r\n\r\n for(; c>47 && c<58 ; c = getchar_unlocked()) {\r\n \tx = (x<<1) + (x<<3) + c - 48;\r\n }\r\n\r\n if(neg)\r\n \tx = -x;\r\n}\r\n\r\ninline void fastRead_string(char *str)\r\n{\r\n register char c = 0;\r\n register int i = 0;\r\n\r\n while (c < 33)\r\n c = getchar_unlocked();\r\n\r\n while (c != '\\n') {\r\n str[i] = c;\r\n c = getchar_unlocked();\r\n i = i + 1;\r\n }\r\n\r\n str[i] = '\0';\r\n}\r\n\r\nint main()\r\n{\r\n\r\n int n;\r\n char s[100];\r\n\r\n fastRead_int(n);\r\n \tprintf("%d\\n", n);\r\n\r\n fastRead_string(s);\r\n \tprintf("%s\\n", s);\r\n return 0;\r\n}\r\n<\/pre>
\nThe solution referrenced is this<\/a>.<\/p>