Summarized some common pointer error-prone issues (3) and pointer Common Problems

Summarized some common pointer error-prone issues (3) and pointer Common Problems

Pointer and string

　　Difference between NULL and NUL: the former is used to represent a special pointer (void *) 0), while the NUL is a char (\ 0) and cannot be mixed.

Character constant: single quotation marks; string: Double quotation marks;

String declaration method: literal, character array, pointer.

String Literal pool:

　　　　　　

String Initialization

Initialize the char array: char header [] = "Media Player ";

　　　　

Strcpy function initialization Array

Char header [13];

Strcpy (header, "Meadia Player ");

2. initialize the char pointer

Char * header; a common method to initialize this string is to use the malloc and strcpy functions to allocate memory and copy the literal to the string.

Char * header = (char *) malloc (strlen ("Media Player") + 1 );

Strcpy (header, "Meadia Player ");

 

Differences between sizeof and strlen:

Standard Input initialization string

Standard string operations

　　　　　　

#include<stdio.h>#include<stdlib.h>#include"string.h"int main(){     char* error="ERROR:";     char* errorMessage="NOT Enough memory";     char* buffer=(char*)malloc(strlen(error)+strlen(errorMessage)+1);     strcpy(buffer,error);     strcat(buffer, errorMessage);    printf("%s",error);    printf("%s\n",errorMessage); } 

Transfer string

　　

#include<stdio.h>#include<stdlib.h>#include"string.h"size_t stringLength(char* string){    size_t length = 0;    while(*(string++))    {        length++;    }    return length; } int main(){     char* error="ERROR: ";     char* errorMessage="NOT Enough memory";     char* buffer=(char*)malloc(strlen(error)+strlen(errorMessage)+1);     strcpy(buffer,error);     strcat(buffer, errorMessage);    printf("%s\n",buffer);    printf("%s\n",error);    printf("%s\n",errorMessage);    printf("%d\n",buffer);    printf("%d\n",stringLength(buffer)); } 

Pointer for passing character constants

Passing parameters to an application

Returns a string.

When a function returns a string, it returns the address of the string. The focus is on returning valid addresses. You can return references to one of the following three objects: character volume, dynamically allocated memory, and local string variables.

Function pointer and string