Question

我是C的新手，现在我正在尝试从文件中提取一些数字到int，但问题是虽然我可以从文件中提取它们并将它们传递给char数组，但我无法转换他们到int，我不知道为什么，所以这里是代码：

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

char *sacardigito(char *vecchar)
{
    char sodigitos[100]={},*ppsodigitos=&sodigitos,*guardarprimeiro=&sodigitos[0];
    do
    {
        if(isdigit(*vecchar)) //if the character inside current address is a digit
        {
            *ppsodigitos=*vecchar; //places the digit inside the char pointer (array sodigitos)
            ppsodigitos++; //increments the pointer
        }
        vecchar++; //increment the pointer address (array vechar)

    }while(*vecchar!='\0');
    printf("\nChar array in function is: %s ",guardarprimeiro); //prints the first position of the array just to make sure only numbers remain
    return guardarprimeiro;
}

int main()
{
    FILE *fp;
    long sonumero;
    int i;
    char vecnumeros[100]={},*retorno;
    fp=fopen("numbers.txt","r"); //open the numbers.txt file
    fgets(vecnumeros,100,(FILE *)fp); //this line passes everything inside to file to a char array
    printf("%s",vecnumeros); //print the char array in order to verify everything is ok
    fclose(fp); //closes the file
    retorno=sacardigito(vecnumeros); //sends to function to retrieve the digits
    printf("\nChar array in main is: %s",retorno); //prints the retuned array
    sscanf(retorno,"%ld",&sonumero); //Convert teh array to digits, I used this function from this user --> http://stackoverflow.com/questions/10204471/convert-char-array-to-a-int-number-in-c
    printf("\nThe numbers in the file are the following: %ld",sonumero); //Now it gives me the error, I don't know why
    return 0;
}

令我感到困惑的是，sscanf并没有将数字转换为long，但在其他代码中，它确实（这是我只是尝试从字母中提取数字，然后是那些来自字符串中的字符）：

char *validacao(char *numeros)
{
    char digitos[100]={},*digitospp=&digitos,*inicio=&digitos;
    do
    {
        if(isdigit(*numeros))
        {
            *digitospp=*numeros;
            digitospp++;
        }
        numeros++;

    }while(*numeros!='\0');
    return inicio;


}
int main()
{
    char numeros[100],*retorno;
    long numeroemint;
    setvbuf(stdout, NULL, _IONBF, 0);   //  Necessario  no  eclipse
    printf("Introduza um numero --> ");
    fgets(numeros,20,stdin);
    retorno=validacao(numeros);
    printf("\nO vector de chars e %s",retorno);
    sscanf(retorno,"%ld",&numeroemint); //esta linha transforma o vector de carcacteres numa variável tipo int
    printf("\nO numero %s so com os digitos e --> %ld",numeros,numeroemint);
    return 0;
}

我错过了什么？

亲切的问候。

编辑：

所以我按照R Sahu的建议更改了代码并且它有效，但我有一个问题。另一位用户说了一些关于未定义的行为和自动变量和指针的内容......有人可以澄清一下吗？那么，指针不仅仅是一个内存地址，而且我不能从函数返回一个内存地址以供以后使用吗？

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

long sacardigito(char *vecchar)
{
    long numeroemint;
    char sodigitos[100]={},*ppsodigitos=&sodigitos[0],*guardarprimeiro=&sodigitos[0];
    do
    {
        if(isdigit(*vecchar)) //if the character inside current address is a digit
        {
            *ppsodigitos=*vecchar; //places the digit inside the char pointer (array sodigitos)
            ppsodigitos++; //increments the pointer
        }
        vecchar++; //increment the pointer address (array vechar)

    }while(*vecchar!='\0');
    printf("\nChar array in function is: %s ",guardarprimeiro); //prints the first position of the array just to make sure only numbers remain
    sscanf(guardarprimeiro, "%ld", &numeroemint);
    printf("\nChar array in function after sscanf is: %ld ",numeroemint);
    return numeroemint;
}

int main()
{
    FILE *fp;
    long retorno;
    char vecnumeros[100]={};
    fp=fopen("numbers.txt","r"); //open the numeros.txt file
    fgets(vecnumeros,100,(FILE *)fp); //this line passes everything inside to file to a char array
    printf("%s",vecnumeros); //print the char array in order to verify everything is ok
    fclose(fp); //closes the file
    retorno=sacardigito(vecnumeros); //sends to function to retrieve the digits
    printf("\nChar array in main is: %ld",retorno); //prints the retuned array
    printf("\nThe numebrs in the file are the following: %ld",retorno); //Now it gives me the error
    return 0;
}

最诚挚的问候。

Answer 1

你有两个问题。首先，您将返回指向仅在函数生命周期内存在的数组的指针，从而导致未定义的行为。其次，你没有用空字符终止字符串。

Answer 2

你已经从@WhozCraig留下的评论中了解了这个问题。

我建议解决问题：

将sacardigito的返回值更改为long

long sacardigito(char *vecchar)
{
    long numeroemint;
    char sodigitos[100]={},*ppsodigitos=&sodigitos,*guardarprimeiro=&sodigitos[0];
    do
    {
        if(isdigit(*vecchar)) //if the character inside current address is a digit
        {
            *ppsodigitos=*vecchar; //places the digit inside the char pointer (array sodigitos)
            ppsodigitos++; //increments the pointer
        }
        vecchar++; //increment the pointer address (array vechar)

    }while(*vecchar!='\0');
    printf("\nChar array in function is: %s ",guardarprimeiro); //prints the first position of the array just to make sure only numbers remain
    sscanf(guardarprimeiro, "%ld", &numeroemint);
    return numeroemint;
}

从文件中提取后，无法将提取的数字转换为int

2 个答案: