Remove first char of string C

问题:

Im trying to remove the first char of the string and keep the remainder, my current code doesnt compile and im confused on how to fix it.

My code:

char * newStr (char * charBuffer)
{
    int len = strlen(charBuffer);
    int i = 1;
    char v;
    if(charBuffer[0] == 'A' || charBuffer[0] == 'Q'){
        for(i=1;i<len;i++)
            v = v + charBuffer[i];
    }
    v = v + '\0';
    return v;
}

Gcc: "Warning: return makes pointer from integer without a cast"

Also: "char * newStr (char * charBuffer)" needs to remain the same.

回答1:

Strings don't work like this in C. You're summing up all of the characters in the buffer into the v variable. You can't use + to concatenate. The code you posted has some serious problems which indicate that there's an understanding gap with how to use C.

Try this:

char *newStr (char *charBuffer) {
  int length = strlen(charBuffer);
  char *str;
  if (length <= 1) {
    str = (char *) malloc(1);
    str[0] = '\0';
  } else {
    str = (char *) malloc(length);
    strcpy(str, &charBuffer[1]);
  }
  return str;
}

or this:

char *newStr (char *charBuffer) {
  char *str;
  if (strlen(charBuffer) == 0)
    str = charBuffer;
  else
    str = charBuffer + 1;
  return str;
}

Depending on whether you want to allocate a new string or not. You'll also have to add the code for handling the cases that don't start with 'Q' or 'A'. I didn't include those because I'm not sure exactly what you're trying to do here.

Make sure you do some research into allocating and deallocating memory with malloc and free. These are fundamental functions to be able to use if you're going to be doing C programming.

回答2:

Well, your description says you want to deal with "strings", but you code deals with char buffers/pointers. The simplest approach to remove the first character for strings would be

const char *newStr(const char *string)
{
    return string+1;
}

but as that doesn't look at all like what your code is doing, you probabaly want something different. For example, if you want to just remove a leading 'A' or 'Q' and then copy the string to a buffer, you want something like

char *newStr(const char *string)
{
    if (string[0] == 'A' || string[0] == 'Q')
        string++;
    return strdup(string);
}

回答3:

You can simply move your char pointer one character in:

char* newstring = oldstring + 1;

回答4:

Your function is declared to return a char * and you are returning a char.

Furthermore, why don't you just return a pointer to the second character?

char * newStr (char * charBuffer)
{
   if (charBuffer && (*charBuffer == 'A' || *charBuffer == 'Q')) return charBuffer + 1;
   return charBuffer;
}

回答5:

Several of the other answers recommended returning charBuffer + 1. As I noted in my previous comment:

This is bad practice. What if the string is dynamically allocated? Perhaps eventually the storage will be freed (starting from the second character). The string should be copied to new storage first.

Freeing a piece of storage from the middle will result in undefined behavior.

Instead, try the strdup function which will return a duplicate of the given string.

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

char *newStr(char* charBuffer) {
    if (charBuffer && (charBuffer[0] == 'A' || charBuffer[0] == 'Q'))
        return strdup(charBuffer + 1);
    else 
        return strdup(charBuffer);
}

void main() {
    char a[7] = "Advait";
    char b[5] = "John";
    printf("%s\n",newStr(a));   // Prints "dvait"
    printf("%s\n",newStr(b));   // Prints "John"
}