{"id":24647,"date":"2022-12-04T16:57:00","date_gmt":"2022-12-04T11:27:00","guid":{"rendered":"https:\/\/jassweb.com\/solved\/solved-reading-an-input-file-in-c\/"},"modified":"2022-12-04T16:57:00","modified_gmt":"2022-12-04T11:27:00","slug":"solved-reading-an-input-file-in-c","status":"publish","type":"post","link":"https:\/\/jassweb.com\/solved\/solved-reading-an-input-file-in-c\/","title":{"rendered":"[Solved] Reading an input file in C++"},"content":{"rendered":"

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doing<\/p>\n

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while (fin >> name >> var1 >> var2 >> var3)\n{\n    cout << name << var1 << var2 << var3 << endl;\n}\n<\/code><\/pre>\n<\/blockquote>\n
you rewrite all the time on the same variables, you need to put the value in a vector as you say in your question<\/p>\n
you need also to check if each input is correct, currently you do not detect the invalid input<\/p>\n
and of course you need to check you open the file<\/p>\n
\n
Example :<\/p>\n
#include <iostream>\n#include <fstream>\n#include <string>\n#include <vector>\n\nint main()\n{\n  std::ifstream fin(\"inputFile.txt\");\n\n  if (!fin.is_open()) {\n    std::cerr << \"cannot open inputFile.txt\" << std::endl;\n    return -1;\n  }\n\n  int numberOfStates, numberOfSymbols, numberOfFinalStates;\n\n  if ((! (fin >> numberOfStates >> numberOfSymbols >> numberOfFinalStates))\n      || (numberOfStates < 0)\n      || (numberOfSymbols < 0)\n      || (numberOfFinalStates < 0)) {\n    std::cerr << \"invalid file\" << std::endl;\n    return -1;\n  }\n\n  \/\/ final states are int, so memorize them in a vector of int\n  \/\/ because their number is known I can size it rather than \n  \/\/ to 'push_back' each value\n  std::vector<int> finalStates(numberOfFinalStates);\n\n  for (int & ft : finalStates) {\n    if (! (fin >> ft)) {\n      std::cerr << \"invalid file reading final states\" << std::endl;\n      return -1;\n    }\n  }\n\n  int numberOfTransitions;\n\n  if (!(fin >> numberOfTransitions) || (numberOfTransitions < 0))  {\n    std::cerr << \"invalid file reading the number of transitions\" << std::endl;\n    return -1;\n  }\n\n  \/\/ you say a transition contains 2 int and a char,\n  \/\/ I define a structure for\n  \/\/ i1 i2 and c are 'poor' names but I don't know their goal\n  struct Transition {\n    int i1, i2; \n    char c;\n  };\n\n  \/\/ the transitions saved in a vector\n  std::vector<Transition> transitions(numberOfTransitions);\n\n  for (Transition & tr : transitions) {\n    if (!(fin >> tr.i1 >> tr.i2 >> tr.c)) {\n      std::cerr << \"invalid file reading transitions\" << std::endl;\n      return -1;\n    }\n  }\n\n  \/\/ print to check\n\n  std::cout << \"numberOfStates=\" << numberOfStates << std::endl;\n  std::cout << \"numberOfSymbols=\" << numberOfSymbols << std::endl;\n  std::cout << \"numberOfFinalStates=\" << numberOfFinalStates << \"\\nfinalStates:\";\n  for (int ft : finalStates) \n     std::cout << ' ' << ft;\n  std::cout << std::endl;\n  std::cout << \"numberOfTransitions=\" << numberOfTransitions\n    << \"\\ntransitions:\" << std::endl;\n  for (const Transition & tr : transitions)\n    std::cout << '\\t' << tr.i1 << ' ' << tr.i2 << ' ' << tr.c << std::endl;\n\n  return 0;\n}\n<\/code><\/pre>\n
Compilation and execution :<\/p>\n
pi@raspberrypi:\/tmp $ g++ -pedantic -Wextra -Wall a.cc\npi@raspberrypi:\/tmp $ cat inputFile.txt\n10 \n3 \n1 \n9 \n12 \n0 1 f \n0 3 f \n1 2 a \n2 9 f \n3 4 f \n3 8 f \n4 5 b \n5 6 f \n6 7 a \n8 9 f \npi@raspberrypi:\/tmp $ .\/a.out\ninvalid file reading transitions\n<\/code><\/pre>\n
The error comes because the file contains only 10 transitions rather than 12 expected, modifying the file to expect 10 transitions :<\/p>\n
pi@raspberrypi:\/tmp $ .\/a.out\nnumberOfStates=10\nnumberOfSymbols=3\nnumberOfFinalStates=1\nfinalStates: 9\nnumberOfTransitions=10\ntransitions:\n    0 1 f\n    0 3 f\n    1 2 a\n    2 9 f\n    3 4 f\n    3 8 f\n    4 5 b\n    5 6 f\n    6 7 a\n    8 9 f\npi@raspberrypi:\/tmp $ \n<\/code><\/pre>\n<\/p><\/div>\n
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            2<\/span> <\/p><\/div>\n<\/div>\n
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solved Reading an input file in C++ <\/p>\n","protected":false},"excerpt":{"rendered":"
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