Home C++ String to int Conversion Using strtol()

String to int Conversion Using strtol()

5. Using For Loop Convert Strings into int

Using the strtol functions: It converts a string to a long integer value, respectively.

Syntax of strtol():

long int strtol(const char* str, char** endptr, int base);

Parameters:

  • str- Pointer to the null-terminated byte string to be converted
  • endptr- Reference to a pointer to character. The function stores the address of the first invalid character in *endptr. If endptr is a null pointer, the function does not store this information.
  • base- The number base to interpret the string. Must be between 2 and 36, inclusive, or 0. If base is 0, the function determines the base from the string itself. If the base is 16, the string may begin with the prefix “0x” or “0X”, in which case the number is parsed as a hexadecimal value.

Return:

  • If the string is empty or does not contain any digits, 0 is returned.
  • If the conversion is successful, the function returns the converted long integer value.
  • If the conversion fails, the function returns 0 and sets *endptr to point to the beginning of the string.   

Example:

C++




#include <stdio.h>
#include <stdlib.h>
 
int main() {
  char str[] = "12345";
  char* endptr;
  long int value = strtol(str, &endptr, 10);
  if (endptr == str) {
    printf("No digits were found\n");
  } else if (*endptr != '\0') {
    printf("Invalid input: %s\n", str);
  } else {
    printf("The value is %ld\n", value);
  }
  return 0;
}
 






                        









																																						

																								

																										
Output


The value is 12345



																																						

																								

																										
Time Complexity: O(N), where N is the number of characters in the string.
Auxiliary Space: O(1)

																																						

																								

																										

																																						

																								

																										

																																						

																								

																										

																																						

																							

											
											

												
Convert String to int in C++

																								

																										
Converting a string to int is one of the most frequently encountered tasks in C++. As both string and int are not in the same object hierarchy, we cannot perform implicit or explicit type casting as we can do in case of double to int or float to int conversion. Conversion is mostly done so that we can convert numbers that are stored as strings.

																																						

																								

																										
Example:

																																						

																								

																										


str=”191″


num=191



																																						

																								

																										
There are 5 significant methods to convert strings to numbers in C++ as follows:

																																						

																								

																										
    

  1. Using stoi() function
    2. 

  2. Using atoi() function
    3. 

  3. Using stringstream
    4. 

  4. Using sscanf() function
    5. 

  5. Using for Loop
    6. 

  6. Using strtol() function
    7. 


																																						

																							

										


										
										

											
Similar Reads

																						

												
													

														1. String to int Conversion Using stoi() Function

													

														The stoi() function in C++ takes a string as an argument and returns its value in integer form. This approach is popular in current versions of C++, as it was first introduced in C++11....
													

												
											

																						

												
													

														2. String to int Conversion Using atoi()

													

														...
													

												
											

																						

												
													

														3. String to int Conversion Using stringstream Class

													

														The atoi() function in C++ takes a character array or string literal as an argument and returns its value in an integer. It is defined in the  header file. This function is inherited by C++ from C language so it only works on C style strings i.e. array of characters....
													

												
											

																						

												
													

														4. Converting String to int Using sscanf()

													

														...
													

												
											

																						

												
													

														5. Using For Loop Convert Strings into int

													

														The stringstream class in C++  allows us to associate a string to be read as if it were a stream. We can use it to easily convert strings of digits into ints, floats, or doubles. The stringstream class is defined inside the  header file....
													

												
											

																						

												
													

														6. String to int Conversion Using strtol()

													

														...
													

												
											

																					


									

									

										
Tags:

																				#CPP-Library
																				#cpp-string
																				#cpp-stringstream
																				#C++
																				#CPP
										
									

									

										

																						
												
												5. Using For Loop Convert Strings into int
											
																					

										

																					

									

								

								

									
Contact Us

									
									
									
								

							

							
						

					

				

			

			

	

		

			

				
				Categories
				
			

			Learn the most popular programming languages in the world.