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reading a text file and searching for a sentence

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reading a text file and searching for a sentence

Dec 16th, 2007

Hello,

i need help on how to search for a sentence inside a txt file after opening it and then applying a condition if that sentence was found.

im a beginner so i don't know how.

basically i have written a program that uses system("command>file.txt") to start a command line process and write the output to a file , and what i want is to search for a certain line in the output (an error message for example) and force the program to act upon the condition of it being found.

 Help with Code Tags 
 c++ Syntax (Toggle Plain Text) 
string sentencetolookup="error connecting to server";
system("command>output.txt");
string sentencetolookup="error connecting to server";
system("command>output.txt");

i want to know how to look for "sentencetolookup" inside the "output.txt" file and if found force the program to stop or return an error message.

any help is appreciated
thanks

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Re: reading a text file and searching for a sentence

Dec 16th, 2007

you need an ifstream object to open the text file, and a string to receive the strings. Both of these are standard c++ classes in <fstream> and <string> header files. There are hundreds, if not thousands, of examples you can follow to write your program so I am not going to repeat them here. Basically you need to (1) read a line using getline function then (2) compare it to the string you are looing for using the == comparison operator.

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Re: reading a text file and searching for a sentence

Dec 16th, 2007

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Originally Posted by Ancient Dragon

you need an ifstream object to open the text file, and a string to receive the strings. Both of these are standard c++ classes in <fstream> and <string> header files. There are hundreds, if not thousands, of examples you can follow to write your program so I am not going to repeat them here. Basically you need to (1) read a line using getline function then (2) compare it to the string you are looing for using the == comparison operator.

thanks, i did view alot of pages talking about ifstream, the best thing i could come up with is read a whole text file , i couldn't find anything on how to read specific lines or read all lines one by one and compare each to a string, all examples showed the use of an array as a buffer to read a txt file instead of a string when i compared an array to a string nothing happened

the whole reason im resorting to txt files is because i couldn't figure out how to obtain any returned results (error or successful completion) by other programs , i am using an exe that renames a computer (netdom) and i have a c++ program that would call that exe using the system() function but i want my program to terminate or loop back to the beginning if the exe file returned an error (like computer account already exists or anything of that sort)

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Re: reading a text file and searching for a sentence

Dec 16th, 2007

You didn't look hard enough. Didn't you run across the getline() method?

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Re: reading a text file and searching for a sentence

Dec 17th, 2007

i did look hard enough to find and use the getline() method , and i was able to read the whole txt file, but i didn't know where to go or what to do after that, how to lookup a sentence by searching each line in the txt file and then if it is found, tell my program do this and that

Last edited by hashinclude; Dec 17th, 2007 at 1:28 am.

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Re: reading a text file and searching for a sentence

Dec 17th, 2007

Maybe this will help. Note the title...

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Re: reading a text file and searching for a sentence

Dec 17th, 2007

in that case can anyone point me to where there is a very detailed tutorial on how to use ifstream ?

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Re: reading a text file and searching for a sentence

Dec 17th, 2007

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Originally Posted by hashinclude

in that case can anyone point me to where there is a very detailed tutorial on how to use ifstream ?

I guess I was too subtle. Post your code as the link describes. Very often if we see the code we can figure out what to tell you. So far we're only guessing.

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Re: reading a text file and searching for a sentence

Dec 17th, 2007

 Help with Code Tags 
 c++ Syntax (Toggle Plain Text) 
int main()
{
 
		char str[5000];
		char errorline[]="grab this text";
		system("command>output.txt");
                fstream file_op("output.txt",ios::in);
		 while(!file_op.eof())
                 {
                         file_op.getline(str,5000);
                         cout <<str;
                 }  
		 if(str==errorline)
		 {
			 cout<<"\nerror found\n";
			 return 0;
		 }
 
		 file_op.close();
                 system("pause");
		 return 0;
 
 
}
int main()
{
	
		char str[5000];
		char errorline[]="grab this text";
		system("command>output.txt");
                fstream file_op("output.txt",ios::in);
		 while(!file_op.eof())
                 {
                         file_op.getline(str,5000);
                         cout <<str;
                 }  
		 if(str==errorline)
		 {
			 cout<<"\nerror found\n";
			 return 0;
		 }

		 file_op.close();
                 system("pause");
		 return 0;


}

you can see that i can only know how to open the file and read it into str array but i don't know how to search the whole file or a certain line or all lines for a string of text that matches errorline

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Re: reading a text file and searching for a sentence

#10

Dec 17th, 2007

line 6: do you have a program on your computer called command.exe ? If not then that line of code will do nothing other than get an error message from the operating system that "command not found".

lines 8 and 10: that loop doesn't work right. You need to combine them like this:

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
while( file_op.getline(str,5000) )
{
    // compare the strings here to see if this line is the one you are looking for
}
while( file_op.getline(str,5000) )
{
    // compare the strings here to see if this line is the one you are looking for
}

line 13: you can not compare two c-style character arrays like that. Use strcpy() to do that
if( strcpy(errorline, str) == 0)

Last edited by Ancient Dragon; Dec 17th, 2007 at 9:03 am.

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