将一个字符串复制到另一个字符串，直到 C 中的某个字符

Question

So, I'm creating a program in c, which works with files. I'm trying to get the string that the user typed until certain character.
For example: the user typed test.txt, I would need the other variable to get all the text until the '.', so the other string would be test
I used strchr, but it gets the string after the point I need, is there any simple method to get the part before the dot?

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

#define MAX 100

int main()
{
    char nome_arquivo[MAX];
    char conteudo[MAX];
    char *nome_backup;

    printf("Nome do arquivo que deseja realizar BACKUP com a extensao: ");
    fgets(nome_arquivo, MAX, stdin);

    //Sempre cuidar com o \n pois ele pode causar erros.
    strtok(nome_arquivo, "\n");

    FILE *arq = fopen(nome_arquivo, "r");

    rewind(arq);
    printf("\nMensagem dentro do arquivo:\n");

    while (fgets(conteudo, MAX, arq) != NULL)
    {
        printf("%s\n",conteudo);
    }

    nome_backup = strchr(nome_arquivo, '.');

    printf("%s\n", nome_backup);

    //FILE *arqbak = fopen(strcat(,".bak"),"w");

}

---

UPDATE:

int main()
{
    char nome_arquivo[MAX];
    char conteudo[MAX];
    char *nome_backup;

    printf("Nome do arquivo que deseja realizar BACKUP com a extensao: ");
    fgets(nome_arquivo, MAX, stdin);

    //Sempre cuidar com o \n pois ele pode causar erros.
    strtok(nome_arquivo, "\n");

    FILE *arq = fopen(nome_arquivo, "r");

    rewind(arq);
    printf("\nMensagem dentro do arquivo:\n");

    while (fgets(conteudo, MAX, arq) != NULL)
    {
        printf("%s\n",conteudo);
    }

    nome_backup = strtok(nome_arquivo, '.');

    printf("%s\n", nome_backup);

    //FILE *arqbak = fopen(strcat(,".bak"),"w");

}

The ERROR is: Segmentantion fault (core dumped)

Answer 1

HI you can you extract string upto "." and store it in different variable.

int main() {

//User input array
char nome_arquivo[MAX];
printf("enter the string:");
scanf("%s",&nome_arquivo);

//Required array
char name[MAX];

//copying string upto "."
for(int i=0; i<MAX; i++) 
{
if (nome_arquivo[i]==".")
break;
else
name[i]=nome_arquivo[i]);
}

// now name consists of your required string
}

Answer 2

You are making it very awkward on yourself. You are doing a good job in using fgets() to handle the input, but you do not need to tokenize the line of input to separate the filename and extension. Instead, (and instead of using strchr() ), use strrchr() to locate the last '.' in the input string. That way if you have a filename that is similar to "somefile.version.ext" you can properly separate the filename into the name "somefile.version" and the extension "ext" .

strrchr will provide a pointer to the final '.' in the input (or NULL if there is no '.' included). There you have the address of the array filled by fgets() and you have the address of the final '.' in that string, all you need to do is subtract the pointer returned by strrchr() and the array filled by fgets() to determined the number of characters to copy. Then a simple call to memcpy is all you need to perform the copy and then nul-terminate the new string at that point.

For example, if you read with fgets() into buf and then want to separate buf into fname holding the filename and ext holding the extension, all you need is:

    char buf[MAXC], fname[MAXC], ext[MAXC], *p;
     ...
    if ((p = strrchr (buf, '.'))) {         /* get pointer to last '.' */
        memcpy (fname, buf, p - buf);       /* copy chars up to last '.' */
        fname[p-buf] = 0;                   /* nul-terminate fname */
        strcpy (ext, p+1);                  /* copy extension */
    }

Notice too, that since you have a pointer to the final '.' , all you need to do is strcpy (ext, p+1); to copy the extension.

A short example putting it altogether, and handling the case where there is no '.' in the filename could be:

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

#define MAXC 1024       /* if you need a constract, #define one (or moare) */ 

int main (void) {

    char buf[MAXC], fname[MAXC], ext[MAXC], *p;

    fputs ("enter filename: ", stdout);     /* prompt for filename */

    if (!fgets(buf, MAXC, stdin)) {         /* read/validate filename */
        fputs ("(user canceled input)\n", stderr);
        return 1;
    }

    buf[strcspn (buf, "\n")] = 0;           /* trim \n from end of buf */

    if ((p = strrchr (buf, '.'))) {         /* get pointer to last '.' */
        memcpy (fname, buf, p - buf);       /* copy chars up to last '.' */
        fname[p-buf] = 0;                   /* nul-terminate fname */
        strcpy (ext, p+1);                  /* copy extension */
    }
    else {  /* no '.' in buf */
        strcpy (fname, buf);                /* copy bur to fname */
        *ext = 0;                           /* make ext empty-string */
    }

    printf ("filename  : %s\n", fname);
    if (*ext)
        printf ("extension : %s\n", ext);
}

( note: you should check that fname isn't the empty-string in order to handle dot-files, etc, .somefile -- that is left to you)

Example Use/Output

$ ./bin/filename_ext
enter filename: somefile.ext
filename  : somefile
extension : ext

What if there is more than one '.' in filename?

$ ./bin/filename_ext
enter filename: somefile.version.ext
filename  : somefile.version
extension : ext

What if there are none?

$ ./bin/filename_ext
enter filename: somefilenoext
filename  : somefilenoext

It is just a much simpler way to approach the separation rather than tokenizing the line. Look things over and let me know if you have questions.

Answer 3

而不是char *nome_backup ，声明应该是char* nome_backup 。