Counting words from argument in C - c

Question

I'm new to C and I try to make a program counting words in a sentence given as arguments when running the program. A word is a character or several seperated by either: ' ', '\n', ',' or '.'. Example: ./words abc abc = 2 words
But I keep getting: "segementation fault(core dumped)". Following is code:
int main(char **argv)
{
char buf[80];
sprintf(buf,"%d words\n",words(argv));
write(1,buf,strlen(buf));
return 0;
}
int words(char **argv)
{
int i=0, sum=0;
while(argv[i] != '\0')
{
if(argv[i] == '.' || argv[i] == ',' || argv[i] == ' ' || argv[i] == '\n')
sum++;
i++;
}
}

Answer 1

Argv is a **char or a pointer to an array of strings. Your code is treating it as if it is a single string so is looping through the pointers to strings and counting them. As none of these pointers is null the program continues beyond the end of the array causing a segfault.

Answer 2

me.c:2:5: warning: first argument of âmainâ should be âintâ [-Wmain]
me.c:2:5: warning: âmainâ takes only zero or two arguments [-Wmain]
me.c: In function âmainâ:
me.c:4:1: warning: implicit declaration of function âwordsâ [-Wimplicit-function-declaration]
me.c:5:1: warning: implicit declaration of function âwriteâ [-Wimplicit-function-declaration]
me.c:5:1: warning: implicit declaration of function âstrlenâ [-Wimplicit-function-declaration]
me.c:5:13: warning: incompatible implicit declaration of built-in function âstrlenâ [enabled by default]
me.c: In function âwordsâ:
me.c:11:16: warning: comparison between pointer and integer [enabled by default]
me.c:11:33: warning: comparison between pointer and integer [enabled by default]
me.c:11:51: warning: comparison between pointer and integer [enabled by default]
me.c:11:69: warning: comparison between pointer and integer [enabled by default]
gcc -Wall filename.c will produces all of the above warnings
These are the warnings in your code. Avoid all. and then try.
Please found Answers for these By searching on google
how to use command line arguments
how to declare a function
how to compare strings and how '.' is differ from "."

Answer 3

If I am not mistaken, then the arguments are automatically split into separate character strings. This is why you get a pointer to a pointer (e.g char ** instead of char*). You are dereferencing the argv array only once. Try this:
while(argv[i] != NULL) {
i++;
}
Second, you wont be able to detect newlines that way, since by definition you cannot pass newline in the arguments. What you probably want to do is parse the input from stdin and invoke your program like this:
echo "abc abc" | ./words
or
./words < SOME_TEXT_FILE
Last but not least your words function does not return anything, it needs to return i:
int words(char** argv) {
//...
return i;
}
That is probably the reason why your program segfaults, since the return value of words() will be NULL and then sprintf will try to dereference the result of the function.
So the whole function needs to look somewhat like this:
int words(char** argv) {
int counter = 0;
while(char[i] != NULL) {
int j = 0;
while(char[i][j] != '\0') {
if(char[i][j] == '.') { //no need to check for '\n'...
counter++;
}
j++;
}
i++;
counter++;
}
return counter;
}

Answer 4

1. Iterate over argv.(having in mind that argv[i] is a pointer to char, argv[0] holds name of the program being executed, and last element of argv is NULL pointer.
2. use strtok function from string.h library to split argv[i] with " .,\n". (every time strtok returns non-NULL value you increment words count).
With some reading on command line arguments and strtok you can easily make it work with any arguments passed.