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How to discard the rest of the characters in a string?

This is a discussion on How to discard the rest of the characters in a string? within the C Programming forums, part of the General Programming Boards category; Dear all: I use fopen() and fgets() to read from a file line by line. I would like to extract ...

  1. #1
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    How to discard the rest of the characters in a string?

    Dear all:

    I use fopen() and fgets() to read from a file line by line. I would like to extract the string in between, for example:

    2013-123-00:12:11 xxxxxxxxxxxxxxxxx

    "00:12:11" is the part I need to extract, any idea how I should go about it?

    I can't use strstr() because the time changes in every line and I tried using strtok() but the result is not what I want.

    Any help is appreciated, thanks.

    hc

  2. #2
    and the hat of wrongness Salem's Avatar
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    So what did you try with strtok()?
    Post your attempt, and then we can tell you what you did wrong (so you learn).

    > 2013-123-00:12:11 xxxxxxxxxxxxxxxxx
    If you use " -" as the delimiter, then you extract in 3 calls
    2013
    123
    00:12:11
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
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  3. #3
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    I would use scanf for this. It has the advantage that it can tell you if a line is not properly formatted (OR if your format string is not specified correctly).

    Example:
    Code:
    char buf[10000];
    while (fgets(buf, 10000, stdin) != NULL) {    
        char mytime[100];
        if (sscanf(buf, "%*[^-]-%*[^-]-%99[^ ]", mytime) == 1) {
            printf("Mytime: %s\n", mytime);
        }
        else {
            printf("Unrecognized string!\n");
        }
    }

  4. #4
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    Quote Originally Posted by Salem View Post
    So what did you try with strtok()?
    Post your attempt, and then we can tell you what you did wrong (so you learn).

    > 2013-123-00:12:11 xxxxxxxxxxxxxxxxx
    If you use " -" as the delimiter, then you extract in 3 calls
    2013
    123
    00:12:11
    I tried with the delimiter ":" and the result was

    2013-123-00
    12
    11

    I'll take your suggestion using -, thanks.

    hc

  5. #5
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    This works, thanks, but there were some weird numbers in between, I'll fix it, thanks very much.

    hc

    Quote Originally Posted by c99tutorial View Post
    I would use scanf for this. It has the advantage that it can tell you if a line is not properly formatted (OR if your format string is not specified correctly).

    Example:
    Code:
    char buf[10000];
    while (fgets(buf, 10000, stdin) != NULL) {    
        char mytime[100];
        if (sscanf(buf, "%*[^-]-%*[^-]-%99[^ ]", mytime) == 1) {
            printf("Mytime: %s\n", mytime);
        }
        else {
            printf("Unrecognized string!\n");
        }
    }

  6. #6
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    Hi, Guys, problem solved, below is the source code, in case anyone running into the same problem, any suggestion to make it "prettier" is appreciated, thanks again.

    Code:
    #include <stdio.h>
    #include <stdlib.h>
    #include <string.h>
    #include <ctype.h>
    
    #define SIZE 50
    #define CROPPED_SIZE 10
    
    /* function prototype */
    char * RemoveColon (char *dest, const char *src);
    
    int main (int argc, char **argv) {
            /* define buffer space for the file */
            char string[SIZE];
            char croppedString[SIZE];
            FILE *pfile;
            int i, previousNum=0, counter=0, timeGap;
            char mytime[CROPPED_SIZE];
            char *croppedTime = mytime;
    
            /* open the existing file from input */
            pfile = fopen (argv[1], "r");
    
            while (fgets (string, SIZE, pfile) != NULL) {
                    strcpy (croppedString, string);
                    /* using sscanf to extract the string */
                    if (sscanf(croppedString, "%*[^-]-%*[^-]-%20[^ ]", mytime) == 1) {
                            /* zero out the unwanted characters */
                            for (i=18; i<SIZE; i++) {
                                    croppedString[i] = '\0';
                            }
                            croppedTime = RemoveColon (croppedTime, mytime);
                            int convertedNum = atoi(croppedTime);
                            timeGap = convertedNum - previousNum;
                            if (timeGap < 0) {
                                    convertedNum = convertedNum + 240000;
                                    timeGap = convertedNum - previousNum;
                            }
                            if ((timeGap >= 10000) && (previousNum != 0)){
                                    counter++;
                                    printf("%s\n", string);
                            }
                            previousNum = convertedNum;
    
                    }
            }
    
            fclose (pfile);
    
            return 0;
    }
    
    
    char * RemoveColon (char *new, const char *str) {
            const char *p;
            char *q;
            for (p=str, q=new; *p != '\0';) {
                    if (*p != ':') {
                            *q = *p;
                            p++;
                            q++;
                    } else {
                            p++;
                    }
            }
            *q = '\0';
            return new;
    }
    Thanks.

    hc

  7. #7
    and the hat of wrongness Salem's Avatar
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    Code:
                            /* zero out the unwanted characters */
                            for (i=18; i<SIZE; i++) {
                                    croppedString[i] = '\0';
                            }
                            croppedTime = RemoveColon (croppedTime, mytime);
                            int convertedNum = atoi(croppedTime);
    I don't know why you need any of this.
    hh:mm:ss should be stored in mytime, as a direct result of the sscanf call.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

  8. #8
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    Because I need to be able to compare and subtract the time with the previous string (record) ...

    Quote Originally Posted by Salem View Post
    Code:
                            /* zero out the unwanted characters */
                            for (i=18; i<SIZE; i++) {
                                    croppedString[i] = '\0';
                            }
                            croppedTime = RemoveColon (croppedTime, mytime);
                            int convertedNum = atoi(croppedTime);
    I don't know why you need any of this.
    hh:mm:ss should be stored in mytime, as a direct result of the sscanf call.

  9. #9
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    I'm not entirely sure what output you want but you're working too hard to get it.
    Code:
    #include <stdio.h>
    #include <ctype.h>
    
    int main(void) {
    
       char s[]={"2013-123-00:12:11 xxxxxxxxxxxxxxxxx"};
       char raw[10]={""};
       char data[10]={""};
       int i,j,n1,n2;
       sscanf(s, "%d%d%s",&n1,&n2,raw);
    
       printf("%d %d raw: %s\n",n1,n2,raw);
       for(i=0,j=0;raw[i];i++) {
          if(isdigit(raw[i])) {
             data[j]=raw[i];
             ++j;
          }
       }
       data[j]='\0';
       printf("\ndata: %s\n",data);
    
       return 0;
    }

  10. #10
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    Yes, you are right ...

    I changed it and it looks better now, thanks for the tip!

    hc


    Quote Originally Posted by Adak View Post
    I'm not entirely sure what output you want but you're working too hard to get it.
    Code:
    #include <stdio.h>
    #include <ctype.h>
    
    int main(void) {
    
       char s[]={"2013-123-00:12:11 xxxxxxxxxxxxxxxxx"};
       char raw[10]={""};
       char data[10]={""};
       int i,j,n1,n2;
       sscanf(s, "%d%d%s",&n1,&n2,raw);
    
       printf("%d %d raw: %s\n",n1,n2,raw);
       for(i=0,j=0;raw[i];i++) {
          if(isdigit(raw[i])) {
             data[j]=raw[i];
             ++j;
          }
       }
       data[j]='\0';
       printf("\ndata: %s\n",data);
    
       return 0;
    }

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