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I am learning C and I want to do this specific task. I know there is a number of similar questions and answers, but still... I will try to be more specific. Lets say, I have a file with following lines:

program01 programs aprogram 1program prog 5program

And I want now an array with:

1program 5program aprogram prog program01 programs

So there are ONLY latin small letters and numbers in strings, no spaces. I know how to perform some separate steps, but want to get and feel the whole (and proper) concept, so to say. Probably it could make some sorting decisions on the fly when reading from file first? Manual sort is preferred for my particular case, just for the sake of better learning and possible optimisation. Lets say, maximal length of one line is 256, maximal number of lines is 256. Thanks in advance.

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    I know how to perform some separate steps, ok show what you know and where are you stuck, and I will be glad to help, as I'm sure other SO users would. Commented Jan 21, 2015 at 16:03
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    1) Read. 2) Sort. Where is the problem? Commented Jan 21, 2015 at 16:05
  • I think you should start with one of the similar questions and adapt it for your own use, after all, they are all basically the same question, but hitting different problems. Commented Jan 21, 2015 at 16:25
  • 1) char buffer[256][256 + 2] 2) call fgets() up to 256 times. 3) qsort(). 4) Print the lines. Commented Jan 21, 2015 at 16:57
  • @iharob (and other) nice that you are glad to help, So I know that char* is just a byte array and I can compare each char just like an int. Would be easy to compare two strings. But I just found it hard to understand some sorting examples due to my lack of C syntax knowledge, especially pointer arithmetic. Commented Jan 21, 2015 at 22:01

3 Answers 3

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Check the below code:

#include <stdio.h> #include<string.h> int main(void) { char a[256][256]; int i=0,j=0,k=0,n; while(i<256 && fgets(a[i],256,stdin) != NULL) { n = strlen(a[i]); if(n >0 && a[i][n-1] == '\n') a[i][n -1] = '\0'; i++; } for(j=0;j<i;j++) { char max[256]; strcpy(max,a[j]); for(k=j+1;k<i;k++) { if(strcmp(a[k],max) < 0) { char tmp[256]; strcpy(tmp,a[k]); strcpy(a[k],max); strcpy(max,tmp); } } strcpy(a[j],max); } for(j=0;j<i;j++) { printf("%s\n",a[j]); } return 0; }
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1 Comment

Comments I made here mostly apply here too. Should a line not fit if(strlen(a[i]) < 255), IMO, better to complain than proceed. Else the split line will be sorted into maybe 2 locations. Suggest insuring i does not exceed 255/6.
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The following cleanly compiles however, I have not tested it you might want to modify it to get the file name from the command line #include <stdio.h> #include <stdlib.h> #include <string.h> #define MAX_ROWS (256) #define MAX_COLUMNS (256) #define FILE_NAME "myInputFile" // prototypes void bubbleSortWordsArray( int wordCount ); void printWordsArray( int wordCount ); static char words[MAX_ROWS][MAX_COLUMNS] = {{'\0','\0'}}; int main(void) { FILE *fp = NULL; if( NULL == (fp = fopen( FILE_NAME, "r") ) ) { perror( "fopen failed" ); exit( EXIT_FAILURE ); } // implied else, fopen successful // read each line from file into entry in words array int i = 0; while( fgets(words[i], MAX_COLUMNS, fp ) ) { // remove trailing newline from string words[i][strlen(words[i])-1] = '\0'; i++; } // 'i' contains number of valid entries in words[][] // sort the array of strings bubbleSortWordsArray(i); printWordsArray(i); return(0); } // end function: main void bubbleSortWordsArray( int wordCount ) { int c; // outer index through rows int d; // inner index through rows char swap[MAX_COLUMNS] = {'\0'}; for (c = 0 ; c < ( wordCount - 1 ); c++) { for (d = 0 ; d < (wordCount - c - 1); d++) { if( 0 > strcmp( words[d], words[d+1] ) ) { // then words need to be swapped strcpy( swap, words[d] ); strcpy( words[d], words[d+1]); strcpy( words[d+1], swap ); } // end if compare/swap } // end for } // end for each row } // end function: bubbleSortWordsArray void printWordsArray( int wordCount ) { int i; // loop index printf( "\n" ); // start on new output line for( i=0; i<wordCount; i++ ) { printf( "%s\n", words[i] ); } } // end function: printWordsArray
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2 Comments

Minor thoughts: 1) Max line length is 256, this usual requires additional buffer space for the '\n' and '\0', 2) words[i][strlen(words[i])-1] is a problem in rare situations when the line begins with an embedded '\0' 3) interesting that code rolled its own sort rather than callingqsort(). 4) Initializing words is not needed - but not bad either.
@chux Also for eg if the buf size is 5 and the input is 1234 then a[i][strlen(a[i]) -1] = '\0' should not be done right so I have the check in my code for the same
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Make a 2D char array try to read it by using fscanf function(sorry i cant remember the syntax). fscan will read your whole line till '\n' but there should not be space and store each string in a row. then sort it by comparaing the first index of each string

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6 Comments

Better to use fgets().
using fgets can be a problem because it picks '\n' with it and can skip some further string. so you have to flush the '\n'.
That is not a problem, it is a task. As for "can skip further string" would you prefer to break your buffer?
"fscan will read your whole line till '\n'" --> no. There is no single fscanf() call that will "read your whole line till '\n". Even fscanf("%[^n]") fails if the line begins with '\n'. Use fgets().
FILE *fp; char a[5][25]; int i=0; fp=fopen("abc.txt","r"); while(!feof(fp)){ fscanf(fp,"%s",a[i]); printf("%s\n",a[i]); i++; } it will read whole line but dont append '\n' and fgets can append with it '\n'
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