Question

好的，有两个问题。首先

Q1。我在运行时分配了足够的内存，仍然连续两次运行案例6后，s1打印垃圾，第三次运行案例6 s1的值消失了

the first image shows the garbage value at the end of string

[第二张图片显示字符串1已消失] [2]

Q2。 STCPY( COPY FUCTION)无效，显示segmentation fault，但我又重新分配了足够的内存。（我需要将s2复制到s1，因此我将L2(string 2's length)重新分配给s1，以免造成内存浪费）

segmentation fault

这里是代码：

#include<iostream>
#include<string>
#include<cstring>

using namespace std;

int STRLEN(char* S){
int i=0;
while(S[i] != '\0'){
    i++;
}
return i;
}

int SUBSTR(char* str1, char* str2){
    //string str1;
    //string str2;
    int L1=0,L2=0;
int i,j,flag=0;
int count=0;
            /*cout<<"\nEnter main string greater characters(str1) : ";
            cin>>str1;

            cout<<"\nEnter phrase to find (str2) : ";
            cin>>str2;
            */
            L1 = STRLEN(str1); //calculate legth of strings
            L2 = STRLEN(str2);
            for(i=0;i<L1;i++){
                count = 0;
                flag = 0;
                for(j=0;j<L2;j+=1){
                    if(str1[i]==str2[j])
                    {
                        //good
                        if(j==L2) //successful phrase's each character 
traversed
                        {
                            break;
                        }
                        i++;
                        count++;
                        //j++;
                    }
                    else
                    {
                        break;
                    }
                } //terminate inner for loops
                {
                    i -= count; //i was incremented explicitly in 
inner loop. for normal operation,
                }               // i has to be decremented by equal 
no. of increments in inner loop
                if(j==L2) //flag for successful traversing of phrase 2 
in string 1
                {
                    flag = 1;
                    break;
                }

            }

            if(flag == 1)
            {
                cout<<"\nSUBTRING PRESENT AT "<<(i+1);
            }
return 0;
}

int STREQL(char* str1, char* str2){
    int flag = 0;
    int L1=0,L2=0;
int i,j;
int count=0;
                      /*  cout<<"\nEnter first word  : ";
            cin>>str1;

            cout<<"\nEnter second word : ";
            cin>>str2;*/
        char* p1;
        char* p2;

    p1 = str1;
        p2 = str2;
        while(*(p1) != '\0')
        {
            if(*(p1) == *(p2))
            {
             //good
             p1++;
             p2++;
            }
            else{
                flag = 1;
                break;
            }
        }
        if(flag == 1 )
        {
            cout<<"\n STRINGS ARE NOT EQUAL";
        }
        else{
            cout<<"\n STRINGS ARE EQUAL";
        }

return 0;
}

int STCPY(char* s1, char* s2){

    int L2 = STRLEN(s2);
    int L1 = STRLEN(s1);
cout<<"\nPASS 1";
        char* s3 = (char*)realloc(s1,L2); //Note :- s3 and s1 point to 
same memory location
cout<<"\nPASS 2";
        while(s2 != '\0')
        {
        *s3 = *s2;
        s3++;
        s2++;
        }
cout<<"\nPASS 3";
s3 -= L2;
s2 -= L2;


cout<<"\n STRING 1 = "<<s1;
cout<<"\n STRING 2 = "<<s2;
return 0;
}

int STRREV(){
return 0;
}

int STRLEN(char* str1, char* str2){
    int L1=0,L2=0;

    L1=STRLEN(str1);
    L2=STRLEN(str2);
    cout<<"\nSTRING 1 LENGTH = "<<L1;
    cout<<"\nSTRING 2 LENGTH = "<<L2;
return 0;
}

int STRCAT(char* s1, char* s2)
{
    int L1=0,L2=0;
    int i,j;

    L1=STRLEN(s1);
    L2=STRLEN(s2);  
    //cout<<"\nSTRING 1 LENGTH = "<<L1;
    //cout<<"\nSTRING 2 LENGTH = "<<L2;

    char* s3 = (char*)realloc(s1,(L1+L2));

int cnt=0;
for(i=L1,s3 = s3+L1; *s2 != '\0'; i++)
{
*s3 = *s2;
s2++;
s3++;
 cnt++;
}
s3 = s3-cnt-L1;
s2 = s2-cnt;
//cout<<"\nConcatenated string s3 =  "<<s3;
//cout<<"\nConcatenated string s1 =  "<<s1;

    cout<<"\nSTRING 1 = "<<s1;
    cout<<"\nSTRING 2 = "<<s2;
return 0;
}

int main(){

int i,j,choice;
char* s1;
char* s2;
cout<<"\nEnter string : ";
s1 = (char*)malloc(50);// ok i made this 50 bytes instead of 10
cin.getline(s1,50);    // cause u guys arguing, but still that doesn't change the output
//cout<<s1;

cout<<"\nEnter string : ";
s2 = (char*)malloc(50);
cin.getline(s2,50);
//cout<<s2;

cout<<"\n------------MENU------------";
cout<<"\n1.SUBSTRING FIND";
cout<<"\n2.EQUAL CHECK";
cout<<"\n3.COPY STRING";
cout<<"\n4.REVERSE";
cout<<"\n5.STRING LENGTH";
cout<<"\n6.STRING CONCATENATION";
cout<<"\n7.EXIT";
cout<<"\n----------------------------";
do{
cout<<"\n\nEnter your choice : ";
cin>>choice;


    switch(choice)
    {
    case 1:
        SUBSTR(s1, s2);    
        break;
    case 2:
            STREQL(s1, s2); 
        break;
    case 3:
        STCPY(s1, s2);
        break;
    case 4:
        STRREV();
        break;
    case 5:
        STRLEN(s1, s2);
        break;
    case 6:
        STRCAT(s1, s2);
        break;
    case 7:
        break;
    }
}while(choice != 7);
return 0;
}

Answer 1

更换＆＃34; PASS 2＆＃34;登录到：

    while(*s2 != '\0')
        {
          *s3 = *s2;
          s3++;
          s2++;
        }

观察s2！=＆＃39; \ 0＆＃39;基本上是指：s2！= nullptr，它永远不会是真的。这就是你出现分段错误的原因。

Answer 2

C字符串以最终\ 0结束。所以内存占用是strlen（str）+ 1个字节。你的STRCAT功能的问题在于你忘了为最终的\ 0添加空间（s3 = realloc（s1，L1 + L2 +1 ），你也忘了添加最终的\ 0（ s3 [L1 + L2] = 0）。您的STCPY函数的同义词，+ s2！= 0替换为* s2！= 0

分段故障和动态内存处理

2 个答案: