为什么我的if语句从未评估过？

Question

I am making a small program in the C90 standard in GCC Ubuntu 10.04 that searches for a word in a line of text and prints out the line if the word is in that line.

My source:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main(){
    int bytesSearch;
    size_t n = 400;
    char *sentence, *word;
    FILE *pFile;

    pFile = fopen("The War of The Worlds.txt","r");

    if (pFile != NULL) {
        puts ("Please enter a search word:");
        sentence = (char *) malloc (n + 1);
        word = (char *) malloc (n + 1);
        bytesSearch = getline(&word, &n, stdin);
        while ((getline(&sentence, &n, pFile)) != -1) {
            char* strResult = strstr(sentence, word);
            if (strResult) {
                printf("%s\n", sentence);
            }
        }
    }
    free(sentence);
    free(word);
    fclose(pFile);
    return EXIT_SUCCESS;
}

My issue is my inner if statement never is true, which I'm assuming means there's something wrong with my strstr function call. Can somebody tell me why that if statement never executes and how to fix it? Thanks!

Answer 1

That's because the string you read from the standard input ends with an unnoticed \\n .

In this case, searching for a word which is at the end of the line will work, whereas searching for a word in the middle of a line will fail, even if it exists.

You might want to remove the trailing newline that is copied into word .

One would usually use something such as the following to do this :

size_t size = strlen(word);
size_t end = size - 1;
if (size > 0 && word[end] == '\n')
    word[end] = '\0';

Answer 2

The man page says:

ssize_t getline(char **lineptr, size_t *n, FILE *stream) reads an entire line from stream, storing the address of the buffer containing the text into *lineptr . The buffer is null- terminated and includes the newline character, if one was found.

So you need to remove the \\n from the end of word before you search it in sentence .

if (pFile != NULL) {
    puts ("Please enter a search word:");
    sentence = (char *) malloc (n + 1);
    word = (char *) malloc (n + 1);
    bytesSearch = getline(&word, &n, stdin);

    if (bytesSearch!=-1) {
        word[strlen(word)-1]='\0'; //removes the '\n' from the word

        while ((getline(&sentence, &n, pFile)) != -1) {
            char* strResult = strstr(sentence, word);
            if (strResult) {
                printf("%s\n", sentence);
            }
        }
    }
    else
        printf("Error taking input!\n");

}

Answer 3

you need to remove the '\\n' at the end read by getline, you can add this code after reading input,

if(word[byteSearch-1]=='\n')
    word[byteSearch-1]='\0';