从 C 中的文件读取时出现奇怪的字符

Question

So I am just trying to learn C and have decided to program a simple calendar where you can add events etc. It is working almost perfectly however, when it tries to read from the file containing the information, the first line contains some strange characters: �<�}�U1.

Code is as follows:

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

void createCalendar(char filename[]) {
    FILE *cptr;
    cptr = fopen(filename, "w");
    char dates[177/sizeof(char)] = "";
    for(int i = 1; i < 32; i++) {
        char strtowrite[7/sizeof(char)] = "";
        sprintf(strtowrite, "%d - \n", i);
        strcat(dates, strtowrite);
    }
    fprintf(cptr, "%s", dates);
    fclose(cptr);
}

void addToDay(char filename[], int day, char event[]) {
    FILE *cptr;
    cptr = fopen(filename, "r");
    char *line = NULL;
    size_t len = 0;
    ssize_t read;
    char dates[177/sizeof(char) + strlen(event)/sizeof(char)];
    int i = 1;
    while ((read = getline(&line, &len, cptr)) != -1) {
        if (i==day) {
            char strtowrite[7/sizeof(char) + strlen(event)/sizeof(char)];
            sprintf(strtowrite, "%d - %s\n", i, event);
            strcat(dates, strtowrite);
        }
        else {
            strcat(dates, line);
        }
        i += 1;
    }
    printf("%s", dates);
    fclose(cptr);
    cptr = fopen(filename, "w");
    fprintf(cptr, "%s", dates);
    fclose(cptr);
}

int main() {
    createCalendar("january");
    addToDay("january", 12, "event");
}

and the first line of output is: í¬_<89>lU1 - (in the file)

Answer 1

Try this

char dates[177/sizeof(char) + strlen(event)/sizeof(char)] = {0};

in your addToDay function when declaring the dates variable. I think that you do not set the memory there, so there might be some junk in that memory location.