为什么我在此while循环中出现分段错误？

每当我执行这个程序时，都会引发分段错误。该程序很简单：计算给定字符串中元音的数量。这是程序：为什么我在此while循环中出现分段错误？

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

int vowelC(char *in, int c){ 
    //Declarations 
    int i; //Dummy index 
    char a; //Temp variable 

    //Validate input 
    if(!in || c == 0) return 1; 

    //Main execution 

    //Convert to all lower case 
    while(in[i] != '\0'){ 
     a=in[i]; 
     if('A' <= a && a <= 'Z') 
       a-= ('A' - 'a'); 
     in[i] = a; 
     i++; 
    } 

    //Count the number of vowels 
    while(!in[i]){ 
      if(in[i] == 'a' || in[i] == 'e' || in[i] == 'i' || in[i] == 'o' || in[i] == 'u') 
        c++; 
    } 
    return 0;      
} 

void printUsage(void){ 
    printf("\n\nThis program will count the number of vowels from an entered character string.\n\t[-c <count>] [-h help]\n\n"); 
} 

int main(int argc, char **argv){ 
    //Declarations 
    int i; //Dummy index 
    int j; //Dummy index 
    int count = 0; 
    int err; 
    int strsize = 0; 

    //Is there at least some user input? 
    if(argc == 1){ 
     printUsage(); 
     return 1; 
} 

//Determine string size if there is more than two user arguments 
for(i=2; i<argc; i++){ 
     strsize += strlen(argv[i]); 
     if (argc > i+1) 
      strsize++; 
} 

//Declare an array of appropriate length to hold the entered strings 
char *in = (char *)malloc(strsize); 

//Validate input 
for(i=1; i<=(argc-2); i++){ 

     //Determine if the user requested usage 
     if(strcmp("-h", argv[i])==0){ 
         printUsage(); 
         return 1; 
     } 

     else if(strcmp("-c", argv[i])==0){ 
         //There must be at least one argument after a call 
         if((i+1) == argc){ 
            printUsage(); 
            return 1; 
         } 
         38 
         //Run another loop to retrieve string inputs 
         for(i=2; i<argc; i++){ 
            for(j=0; j != '\0'; j++){//Determine if a sting is really a string 
              if(isalpha(argv[i][j])){ 
                    printUsage(); 
                    return 1; 
              } 
          } 
          strcat(in, argv[i]); 
          if(argc > (i+1)) 
          strcat(in, " "); 
          } 

     } 

     else{//Unknown input 
         printUsage(); 
         return -1; 
     } 

//For bracket 
} 

err = vowelC(in, count); 
assert(!err); 
printf("\n\nThe number of vowels counted is %d.\n\nPlease press enter to exit...", count); 
getchar(); 
return 0; 
//Main Bracket  
}

GDB报告在while(in[i] != '\0')发生分段故障。然而，原因没有我。任何见解都会被赞赏。

来源

2013-10-04 Mlagma

如果代码已经在（'-Wall -Wextra -pedantic'）上编译了所有警告，编译器会警告*'i'可能使用了未初始化*。 – alk

这显然是一个学生的问题，我敢说他发现这个特殊的错误非常有教育意义。他经历了一个错误，这是真正问题的后果，他学习了关于段错误的知识，他学习了如何存储数组，关于初始化变量的重要性，关于编译时没有警告的危险...... –