分配错误分配

我目前正在学习C，而我来自java。 我们的任务要求我们从可以添加的文件中计算字符串，或者要求用户输入字符串。 我们刚开始使用指针，并且查找了段错误发生的不同原因，但我不知道如何检查它是哪个问题。 我将所有的指针初始化为NULL，但它仍然不起作用，从我读到的这是发生分段错误的最常见原因。

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

int debug = 0;

int
main(int argc, char **argv)
{
    extern char *optarg;
    extern int optind;
    FILE* infile = NULL;
    int c, err = 0; 
    int lflag = 0, sflag = 0, count = 0; //flags and count
    char *shortWord = NULL, *longWord = NULL; //variable for shortest and longest word
    int shortest = 100, longest = 0; //longest char 100, shortest 0
    char *string = NULL;
    char *pch = NULL;
    static char usage[] = "usage: %s [-l] [-s] [filename]n";

    while ((c = getopt(argc, argv, "ls")) != -1)
        switch (c) 
        {
            case 'l':
                lflag  = 1;
                break;
            case 's':
                sflag = 1;
                break; 
            case '?':
                err = 1;
                break;
        }

    if (err) 
    {
        fprintf(stderr, usage, argv[0]);
        exit(1);
    }
    //checks for file and then runs loop for word count
    infile = fopen("myfile.txt","r");
    if (infile != NULL)
    {
        fgets(string, 100, infile);
        pch = strtok (string, " ,.-");
        while(pch != NULL)
        {
            count++;
            if (strlen(pch) > longest)
                longWord = pch;
            if (strlen(pch) < shortest)
                shortWord = pch;
            pch = strtok (NULL, " ,.");
        }
    } 
    //else, asks for string
    else
    {
        printf("Enter your string: n");
        fgets(string, 100, stdin);
        int len = strlen(string);
        count = len;
        pch = strtok ( string, " ,.-");
        while(pch != NULL)
        {
            count++;
            if (strlen(pch) > longest)
                longWord = pch;
            if (strlen(pch) < shortest)
                shortWord = pch;
            pch = strtok (NULL, " ,.");
        }   
    }

    //following lines compute value based on arguments
    if(lflag == 1)
    {
        printf("Longest word is %s", longWord);
    }
    if(sflag ==  1)
    {
        printf("Shortest word is %s", shortWord);
    }

    printf("Word count = %.2dn", count);

    exit(0);
}

他们是你的代码中的一些问题：

 infile = fopen("myfile.txt", "r");
 if (infile == NULL) {
     fprintf(stderr, "Failed to open filen");
     exit(EXIT_FAILURE);
 }

case '?':
    err = 1;
    break;

default:
    fprintf(stderr, "usage: %s [-l] [-s] [filename]n", argv[0]);
    exit(EXIT_FAILURE);

以下是一些演示这些要点的示例代码：

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

#define LINESIZE 100

void longest_shortest_words(char line[], char **longest, char **shortest, size_t *wordcount);
void print_output(int lflag, int sflag, char *longword, char *shortword, size_t wordcount);
void remove_newline(char line[]);

int main(int argc, char * const argv[]) {
    FILE *infile;
    char line[LINESIZE] = {''};
    int opt, sflag = 0, lflag = 0;
    size_t wordcount = 0;
    const char *optstr = "ls";
    char *longword = NULL, *shortword = NULL;

    while ((opt = getopt(argc, argv, optstr)) != -1) {
        switch(opt) {
            case 'l':
                lflag = 1;
                break;
            case 's':
                sflag = 1;
                break;
            default:
                fprintf(stderr, "usage: %s [-l] [-s] [filename]n", argv[0]); 
                exit(EXIT_FAILURE);
        }
    }

    /* Checking if file is in directory */
    infile = fopen("myfile.txt", "r");
    if (infile == NULL) {
        fprintf(stderr, "Failed to open filen");
        exit(EXIT_FAILURE);
    }

    /* checking if line exists in file */
    if (fgets(line, LINESIZE, infile) == NULL) {
        fprintf(stderr, "No line found in file.n");

        printf("nEnter string instead:n");
        if (fgets(line, LINESIZE, stdin) != NULL) {
            remove_newline(line);
            longest_shortest_words(line, &longword, &shortword, &wordcount);   
            /* checking that longWord, shortWord and word_count are valid */
            if (longword != NULL && shortword != NULL && wordcount > 0) {
                print_output(lflag, sflag, longword, shortword, wordcount);
            }
        }

    /* file has line, do stuff with it */
    } else {
        remove_newline(line);
        longest_shortest_words(line, &longword, &shortword, &wordcount);
        print_output(lflag, sflag, longword, shortword, wordcount);
    }

    exit(EXIT_SUCCESS);
}

/* function for printing output, can be improved */
void print_output(int lflag, int sflag, char *longword, char *shortword, size_t wordcount) {
    if (lflag) {
        printf("Longest word: %sn", longword);
    }

    if (sflag) {
        printf("Shortest word: %sn", shortword);
    }

    if (wordcount > 0) {
        printf("Word count = %zun", wordcount);
    }
}

/* function for removing newline, and checking that input hasnt exceeded limit */
void remove_newline(char line[]) {
    size_t slen;

    slen = strlen(line);
    if (slen > 0 && line[slen-1] == 'n') {
        line[slen-1] = '';
    } else {
        fprintf(stderr, "nToo many characters in input.n");
        exit(EXIT_FAILURE);
    }
}

/* function which parses line, and saves longWord and shortWord in pointers */
void longest_shortest_words(char line[], char **longword, char **shortword, size_t *wordcount) {
    char *word = NULL;
    const char *delim = " ,.";

    word = strtok(line, delim);
    if (word != NULL) {
        *longword = word;
        *shortword = word;
        *wordcount = 1;
    }

    while ((word = strtok(NULL, delim)) != NULL) {
        (*wordcount)++;
        if (strlen(word) > strlen(*longword)) {
            *longword = word;
        } else if (strlen(word) < strlen(*shortword)) {
            *shortword = word;
        } 
    }
}

注意：上面显示的代码可以改进，只是向您展示解决问题的另一种方法。

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