C函数中随机更改值的字符串

Question

我正在尝试编写一种方法将表示日期的C字符串转换为不同的格式。

/* 
Takes in a date of the format MM/DD/YYYY-HR:MN, 
and converts it to YYYYDDMMHRMN format. 
*/ 

void convertFormattedDate(char** date){ 
char* dateHelper = calloc(strlen(*date), sizeof(char)); 
strcpy(dateHelper, *date); 
const char * delims = "/-:"; 

char* formattedDate = calloc(12+1, sizeof(char)); //leaving space for null terminator 

char* token = strtok(dateHelper, delims); 

//yes I know this is hacky and terrible 
char* month = NULL; 
char* day = NULL; 
char* year = NULL; 
char* hr = NULL; 
char* mn = NULL; 

int index=0; 
while (token!=NULL) { 
    switch (index) { 
     case 0: 
      month = token; 
      break; 
     case 1: 
      day = token; 
      break; 
     case 2: 
      year = token; 
      break; 
     case 3: 
      hr = token; 
      break; 
     case 4: 
      mn = token; 
      break; 
     default: 
      printf("Something weird has happened"); 
      break; 
    } 
    token = strtok(NULL, delims); 
    index++; 
} 
strcat(formattedDate, year); 
strcat(formattedDate, month); 
strcat(formattedDate, day); 
strcat(formattedDate, hr); 
strcat(formattedDate, mn); 

*date = formattedDate; 
} 

当我尝试调用

char* date = "10/24/1994-23:14"; 
convertFormattedDate(&date); 

事情做工精细，直到我开始串联年，月，日等为格式化的日期。我打电话给 strcat（formattedDate，year）;

和步骤，通过我的代码，MN的值突然变得

时，只应

有谁知道为什么调用strcat可能会影响其他变量或者我应该怎么做才能防止这种情况发生？

Answer 1

保持简单：

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

/* 
Takes in a date of the format MM/DD/YYYY-HR:MN, 
and converts it to YYYYDDMMHRMN format. 
*/ 

void convertFormattedDate(char* date){ 
    char* dateHelper = strdup(date); 

    dateHelper[0] = date[6]; 
    dateHelper[1] = date[7]; 
    dateHelper[2] = date[8]; 
    dateHelper[3] = date[9]; 

    dateHelper[4] = date[3]; 
    dateHelper[5] = date[4]; 

    dateHelper[6] = date[0]; 
    dateHelper[7] = date[1]; 

    dateHelper[8] = date[11]; 
    dateHelper[9] = date[12]; 
    dateHelper[10] = date[14]; 
    dateHelper[11] = date[15]; 

    dateHelper[12] = '\0'; 
    strcpy(date, dateHelper); 
    free(dateHelper); 
} 

int main(void) 
{ 
    char dt[] = "10/21/2015-00:19"; 
    convertFormattedDate(dt); 
    printf("%s\n", dt); 
    return 0; 
} 

程序输出

201521100019