我在函数中使用此代码来获取文件中最短和最长的字符串 . 长度变量和字符串在循环外声明 . int 变量在循环内部和外部正确更新，但 char* 变量仅在内部正确更新 .
在我得到的最后一个printf语句中：
the string Zulia
is the longest in a2.txt and has 18 chars
the string Zulia
is the shortest in a2.txt and has 5 chars
这里发生了什么？
fp1 = fopen(fileName, "r");
if (fp1 == NULL)
{
printf("Error while opening file: %s\n",fileName);
exit (1);
}
int lengthLongestString=1;
int lengthShortestString=1000;
int lengthActualString=0;
char *longestString;
char *shortestString;
char *currentString;
while (fgets(fileLine, SIZE_OF_LINE, fp1) != NULL)
{
if(((strcmp(fileLine, "\n") != 0)) && (strcmp(fileLine, "\r\n") != 0)){ //Validates against storing empty lines
lineas[numeroLineas++] = strdup(fileLine);
lengthActualString=strlen(fileLine);
currentString=fileLine;
if (lengthActualString>lengthLongestString){
lengthLongestString = lengthActualString;
longestString=fileLine;
printf("the longest string now is %s \n",longestString);
}
else if (lengthActualString<lengthShortestString){
lengthShortestString = lengthActualString;
shortestString=fileLine;
printf("the shortest string now is %s \n",shortestString);
} // END IF
}// END IF
} //END WHILE
printf("the string %s is the longest in %s and has %d chars\n",longestString, fileName, lengthLongestString );
printf("the string %s is the shortest in %s and has %d chars\n",shortestString, fileName, lengthShortestString);
3 回答
longestString和shortestString是指针 . 他们 point 某个地方 . 当然，如果你改变某个地方的内容，那么指针指向的东西就会改变:-)您需要为
longestString和shortestString分配内存（或将它们定义为数组而不是指针）并将字符复制到那里 .您复制了字符串，但忘记将该副本分配给最短/最长的字符串变量，而是分配指向读取缓冲区的指针 .
那是因为您将
shortestString和longestString分配给fileLine. 因此，您始终在fileLine中打印该值，该内容是您使用fgets读取的最后一行的内容 .你应该阅读指针 .