search for a string in a file using C

[mnNewbie]

I need to basically rewrite grep command:

method is suppose to take an exact string and an exact filename as the 2 arguments
grep<string><filename>
then it has to search through the file for the string and print out the "line" and the "line number" the string is in.
example #grep matt students
12 the student matt was late for class today
35 when class started matt was just walking in the door

Im using some code from a website.
This is what I have so far, but I've been working on asking the user for the filename to look at and I keep getting a seg fault. I feel like Im using the scanf() for the file improperly, also I believe I allocated enough memory for the file

#include <stdio.h>

const unsigned MAXLINE=9999;



char * skip_ws(char *line)
{
    return line+strspn(line," \t");
}

char * findval(char *line,char const* prefix)
{
    char *p;
    int prelen;
    prelen = malloc(strlen(prefix));
    p=skip_ws(line);
    if (strncmp(p,prefix,prelen)==0)
        return p+prelen;
    else
        return NULL;
}

char *findval_slow(char *line,char const* prefix)
{
    return findval(line,prefix);
}

int main() {
    
    char line[MAXLINE];
    char *p,*pend;
    int findlen;
    FILE *ifp;
    char *string;
    char filename[100];
    long lsize;
    char *buffer;
    size_t result;


    printf("what file do you want to look at\n");
     scanf("%c", &filename);
    ifp = fopen(&filename, "r");
    if(ifp = NULL){
      fprintf(stderr, "Cant open input file!\n");
      exit(1);
    }

    //obtain file size
    fseek(ifp, 0, SEEK_SET);
    lsize = ftell(ifp);
    printf("the file size is = %ld", lsize);
    rewind(ifp);

    //allocate memory to contain whole file
    buffer = (char*) malloc (sizeof(char)*lsize);
    if(buffer == NULL){
      fputs ("memory error", stderr);
      exit(2);
    }

    // copy the file into the buffer
    result = fread(buffer, 1, lsize, ifp);

    puts(buffer);
    if(result != lsize){
      fputs ("reading error", stderr);
      exit(3);
    }


    printf("what string do you want to search for?\n");
    scanf("%s", string);

    findlen= strlen(string);


    while (p=fgets(line,MAXLINE,ifp)) {
       printf("Looking at %s\n",p);
       if (p=findval(line,string)) {
            pend=p+strlen(p)-1; /* check last char for newline terminator */
            if (*pend=='\n') *pend=0;
            printf("Found %s\n",p); 
        }
    }
    return 0;
}

[Ancient Dragon]

line 43, the scanf() is wrong. Use "%s" (for string), not "%c" (for a single character). scanf() will not work at all if there are spaces in the filename. In that case call fgets() instead of scanf(), e.g. fgets(filename, sizeof(filename), stdin); Then you will have to remove the '\n' that fgets() puts at the end of the string.

[mnNewbie]

Thanks for the help!
so I change to fgets() and then check to see if filename has '\n' at the end and then set it to 0 if it does. Im still getting a seg fault after it take the file in. :(

[WaltP]

I need to basically rewrite grep command:

method is suppose to take an exact string and an exact filename as the 2 arguments
grep<string><filename>
then it has to search through the file for the string and print out the "line" and the "line number" the string is in.
example #grep matt students
12 the student matt was late for class today
35 when class started matt was just walking in the door

Im using some code from a website.

There's your first problem. You don't know C well enough to modify existing code to try using someone else's code as a starting point. Therefore, start over and take it a step at a time.

1) Input, and display the 2 values. When this runs without error...
2) Open the file name specified in the FILENAME parameter. When you get this correct (complete with error processing)...
3) Read the file line by line in a loop and display each line.
Continue until the program is running as you wish.